#define DONE 1147797409030816545

#include <sstream>
#include <iostream>
#include <queue>

using namespace std;

const unsigned long long Masks[] = {
        0x000000000000000F,
        0x00000000000000F0,
        0x0000000000000F00,
        0x000000000000F000,
        0x00000000000F0000,
        0x0000000000F00000,
        0x000000000F000000,
        0x00000000F0000000,
        0x0000000F00000000,
        0x000000F000000000,
        0x00000F0000000000,
        0x0000F00000000000,
        0x000F000000000000,
        0x00F0000000000000,
        0x0F00000000000000,
        0xF000000000000000,
};
const unsigned long long AntiMasks[] = {
        0xFFFFFFFFFFFFFFF0,
        0xFFFFFFFFFFFFFF0F,
        0xFFFFFFFFFFFFF0FF,
        0xFFFFFFFFFFFF0FFF,
        0xFFFFFFFFFFF0FFFF,
        0xFFFFFFFFFF0FFFFF,
        0xFFFFFFFFF0FFFFFF,
        0xFFFFFFFF0FFFFFFF,
        0xFFFFFFF0FFFFFFFF,
        0xFFFFFF0FFFFFFFFF,
        0xFFFFF0FFFFFFFFFF,
        0xFFFF0FFFFFFFFFFF,
        0xFFF0FFFFFFFFFFFF,
        0xFF0FFFFFFFFFFFFF,
        0xF0FFFFFFFFFFFFFF,
        0x0FFFFFFFFFFFFFFF
};

struct Puzzle {
    unsigned long long data; //Само состояние
    string Prev; // Предки;
    unsigned long long Dist; //Расстояние до конечнего расстояния
    int ZeroPos; //Положение нуля
    unsigned long long Father; //

    Puzzle(string P) : Prev(P), Dist(0), Father(0), ZeroPos(0) {}

    void setAt(int place, unsigned char value);

    unsigned char getAt(int place) const;

    //Эврестика
    unsigned long long Heueristic();

    void Distance();
};

void Puzzle::setAt(int place, unsigned char value) {
    data = (data & AntiMasks[place]) | (static_cast<long long>( value ) << (place << 2));
}

unsigned char Puzzle::getAt(int place) const {
    return static_cast<unsigned char>((data & Masks[place]) >> (place << 2));
}

//Эврестика
unsigned long long Puzzle::Heueristic() {
    unsigned long long h = 0;
    for (int i = 0; i < 16; i++) {
        char value = getAt(i);
        if (value != 0) {
            int targetX = (value - 1) / 4; // expected x-coordinate (row)
            int targetY = (value - 1) % 4; // expected y-coordinate (col)
            int dx = i / 4 - targetX; // x-distance to expected coordinate
            int dy = i % 4 - targetY; // y-distance to expected coordinate
            h += (abs(dx) + abs(dy));
        }
    }
    return h;
}

void Puzzle::Distance() {
    Dist = Prev.size() + Heueristic();
}

//Движение вправо
Puzzle MoveRight(Puzzle l) {
    int pos = l.ZeroPos;
    unsigned char k = l.getAt(pos + 1);
    l.setAt(pos, k);
    l.setAt(pos + 1, 0);
    l.ZeroPos++;
    l.Prev = l.Prev + 'L';
    l.Distance();
    return l;
}

//Движение влево
Puzzle MoveLeft(Puzzle l) {
    int pos = l.ZeroPos;
    unsigned char k = l.getAt(pos - 1);
    l.setAt(pos, k);
    l.setAt(pos - 1, 0);
    l.ZeroPos--;
    l.Prev = l.Prev + 'R';
    l.Distance();
    return l;
}

//Движение вверх
Puzzle MoveUp(Puzzle l) {
    int pos = l.ZeroPos;
    unsigned char k = l.getAt(pos - 4);
    l.setAt(pos, k);
    l.setAt(pos - 4, 0);
    l.ZeroPos -= 4;
    l.Prev = l.Prev + 'D';
    l.Distance();
    return l;
}

//Движение вниз
Puzzle MoveDown(Puzzle l) {
    int pos = l.ZeroPos;
    unsigned char k = l.getAt(pos + 4);
    l.setAt(pos, k);
    l.setAt(pos + 4, 0);
    l.ZeroPos += 4;
    l.Prev = l.Prev + 'U';
    l.Distance();
    return l;
}

//Получаем список всех состояний, в которые можно перейти из нынешнего
vector<Puzzle> getNodes(Puzzle tmp) {
    vector<Puzzle> ToReturn;
    int pos = tmp.ZeroPos;
    if (pos >= 4) {
        Puzzle toPush = MoveUp(tmp);
        if (tmp.Father != toPush.data) {
            ToReturn.push_back(toPush);
        }
    }
    if (pos <= 11) {
        Puzzle toPush = MoveDown(tmp);
        if (tmp.Father != toPush.data) {
            ToReturn.push_back(toPush);
        }
    }
    if (pos % 4 != 3) {
        Puzzle toPush = MoveRight(tmp);
        if (tmp.Father != toPush.data) {
            ToReturn.push_back(toPush);
        }
    }
    if (pos % 4 != 0) {
        Puzzle toPush = MoveLeft(tmp);
        if (tmp.Father != toPush.data) {
            ToReturn.push_back(toPush);
        }
    }
    return ToReturn;
}

//Функция поиска для IDA
Puzzle Search(Puzzle node, unsigned long long bound) {
    if (node.Dist > bound) {
        return node;
    }
    if (node.data == DONE) {
        return node;
    }
    Puzzle min("");
    min.Dist = 100000000;
    vector<Puzzle> vert = getNodes(node);
    for (int i = 0; i < vert.size(); i++) {
        Puzzle tmp = Search(vert[i], bound);
        if (tmp.data == DONE) {
            return tmp;
        }
        if (tmp.Dist < min.Dist) {
            min = tmp;
        }
    }
    return min;
}

//Решается ли данное состояние
bool IsSolved(Puzzle start) {
    int mistakes = start.ZeroPos / 4 + 1; //Переменная для подсчета счетности
    for (int i = 0; i < 16; i++) {
        for (int j = i + 1; j < 16; j++) {
            int f1 = i / 4;
            int f2 = i % 4;
            int s1 = j / 4;
            int s2 = j % 4;

            int first = start.getAt(f1 * 4 + f2);
            int second = start.getAt(s1 * 4 + s2);
            if (first != 0 && second != 0) {
                if (first > second) {
                    mistakes++;
                }
            }
        }
    }
    if (mistakes % 2 != 0) {
        return false;
    }
    return true;
}

string IDA(Puzzle start) {
    start.Distance();
    unsigned long long bound = start.Dist;
    while (1) {
        Puzzle tmp = Search(start, bound);
        if (tmp.data == DONE) {
            return tmp.Prev;
        }
        bound = tmp.Dist;
    }
}

int main() {
    Puzzle start(""); //Начальное состояние

    //Считываем состояние
    int ZeroPos = 0;
    for (int i = 0; i < 16; i++) {
        int Input;
        cin >> Input;
        start.setAt(i, Input);
        if (Input == 0) {
            ZeroPos = i;
        }
    }
    start.ZeroPos = ZeroPos;

    //Проверяем на решаемость
    if (!IsSolved(start)) {
        cout << "-1";
        return 0;
    }

    //Если решается, то находим ответ и выводим
    string answer = IDA(start);
    cout << answer.length();
    cout << "\n";
    cout << answer;
    return 0;
}