#define DONE 1147797409030816545

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

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
};
//Состояние
struct Puzzle {
    unsigned long long data; // sequence
    string Prev; // Prev;
    int Dist;
    int ZeroPos;

    Puzzle(string P);

    void setAt(int place, unsigned char value);

    unsigned char getAt(int place) const;

    void Distance();
};

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


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));
}

void Puzzle::Distance() {
    Dist = 0;
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4; j++) {
            int value = getAt(4 * i + j);
            if (value != 0) {
                int targetX = (value - 1) / 4;
                int targetY = (value - 1) % 4;
                int dx = i - targetX;
                int dy = j - targetY;
                Dist += abs(dx) + abs(dy);
            }
        }
    }
}

bool Compare(Puzzle first, Puzzle second) {
    return first.Dist > second.Dist;
}

Puzzle MoveRight(const Puzzle& old) {
    Puzzle result(old.Prev + 'L');
    result.data = old.data;

    int pos = old.ZeroPos;
    unsigned char k = old.getAt(pos + 1);
    result.setAt(pos, k);
    result.setAt(pos + 1, 0);
    result.ZeroPos = pos + 1;
    return result;
}

Puzzle MoveLeft(const Puzzle& old) {
    Puzzle result(old.Prev + 'R');
    result.data = old.data;

    int pos = old.ZeroPos;
    unsigned char k = old.getAt(pos - 1);
    result.setAt(pos, k);
    result.setAt(pos - 1, 0);
    result.ZeroPos = pos - 1;
    return result;
}

Puzzle MoveUp(const Puzzle& old) {
    Puzzle result(old.Prev + 'D');
    result.data = old.data;

    int pos = old.ZeroPos;
    unsigned char k = old.getAt(pos - 4);
    result.setAt(pos, k);
    result.setAt(pos - 4, 0);
    result.ZeroPos = pos - 4;
    return result;
}

Puzzle MoveDown(const Puzzle& old) {
    Puzzle result(old.Prev + 'U');
    result.data = old.data;

    int pos = old.ZeroPos;
    unsigned char k = old.getAt(pos + 4);
    result.setAt(pos, k);
    result.setAt(pos + 4, 0);
    result.ZeroPos = pos + 4;
    return result;
}
//Решается ли
bool IsSolved(const Puzzle& node) {
    int mistakes = node.ZeroPos / 4 + 1; //Переменная для подсчета счетности
    for (int i = 0; i < 16; i++) {
        for (int j = i + 1; j < 16; j++) {
            const int f1 = i / 4;
            const int f2 = i % 4;
            const int s1 = j / 4;
            const int s2 = j % 4;

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

//А*
string AStar(Puzzle start) {
    unordered_set<unsigned long long> S;
    priority_queue<Puzzle, vector<Puzzle>, bool (*)(Puzzle, Puzzle)> q(Compare); //Приоритетная очередь с сравнием для вывода минимального
    start.Distance();

    q.push(start);
    while (!q.empty()) {
        Puzzle tmp = q.top();
        q.pop();
        if (tmp.data == DONE) {
            return tmp.Prev;
        }
        S.insert(tmp.data);
        int pos = tmp.ZeroPos;
        if (pos >= 4) {
            Puzzle toPush = MoveUp(tmp);
            auto find = S.find(toPush.data);
            if (find == S.end()) {
                q.push(toPush);
            }
        }
        if (pos <= 11) {
            Puzzle toPush = MoveDown(tmp);
            auto find = S.find(toPush.data);
            if (find == S.end()) {
                q.push(toPush);
            }
        }
        if (pos % 4 != 3) {
            Puzzle toPush = MoveRight(tmp);
            auto find = S.find(toPush.data);
            if (find == S.end()) {
                q.push(toPush);
            }
        }
        if (pos % 4 != 0) {
            Puzzle toPush = MoveLeft(tmp);
            auto find = S.find(toPush.data);
            if (find == S.end()) {
                q.push(toPush);
            }
        }
    }
}

int main() {
    //Оптимизация ввода
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    //Считываем начальное состояние
    Puzzle start("");
    int ZeroPos = 0;
    for (int i = 0; i < 16; i++) {
        int Input = 0;
        scanf("%i", &Input);
        start.setAt(i, static_cast<unsigned char>(Input));
        if (Input == 0) {
            ZeroPos = i;
        }
    }
    start.ZeroPos = ZeroPos;

    //Проверяем есть ли решение
    bool WillGo = IsSolved(start);
    if (!WillGo) { //Если нет решения
        cout << "-1";
        return 0;
    }
    //Иначе запускаем A*
    string answer = AStar(start);
    cout << answer.size();
    cout << "\n";
    cout << answer;

    return 0;
}