#include <iostream>
#include <vector>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <map>

using namespace std;

const int n = 1000, m = 1000;

dx[8] = {-1, 0, 1, 1, 1, 0, -1, -1};
dy[8] = {1, 1, 1, 0, -1, -1, -1, 0};

double sqr(double a) {
    return a * a;
}

double f(const pair<int, int> &coord) {
    double x = coord.first / 500, y = coord.second / 500;
    return exp(-sqr(x - 1) - sqr(y - 1));
    // return exp(- x * x - y * y) * (sin(100 * x * x) + 1) * (-cos(100 * y * y) + 1);
    // return exp(-5*sqr(x-0.2)-5*sqr(y-0.5))+exp(-sqr(x-2)-sqr(y))+exp(-5*sqr(x-1.3)-5*sqr(y-0.8))+exp(-5*sqr(x-1.5)-5*sqr(y-0.1));
}

double eval_time_point(const pair<int, int> &coord) {
    return f(coord);
}

bool check(const vector<pair<int, int> > &path) {
    if (path[0].first != 0 || path[0].second != 0 ||
        path[path.size() - 1].first != n || path[path.size() - 1].second != m) {
        return false;
    }

    for (int i = 0; i < path.size() - 1; ++i) {
        if (abs(path[i].first - path[i + 1].first) > 1 ||
            abs(path[i].second - path[i + 1].second) > 1) {
            return false;
        }
    }

    return true;
}

double eval_time_path(const vector < pair<int, int> > &path) {
    if (!check(path)) {
        return -1;
    }
    double time = 0;
    for (auto &coord: path) {
        time += f(coord);
    }
    return time;
}

vector < pair<int, int> > generate_path() {

    vector < pair<int, int> > best_path;
    double best_time = 1E+9;

    for (int i = 0; i < 5; ++i){
        vector < pair<int, int> > path;
        pair<int, int> current_coord(0, 0);

        path.push_back(current_coord);
        map <int, pair<int, int> > max_coords;
        map <int, pair<int, int> > n_points;
        for(int i = 0; i < 8; i++){
            current_coord.first = current_coord.first+dx[i];
            current_coord.second = current_coord.second+dy[i];
            max_coords.insert( eval_time_point(current_coord), make_pair(current_coord.first, current_coord.second));

            n_point[time] = make_pair();
        }

        if (eval_time_path(path) < best_time) {
            best_time = eval_time_path(path);
            best_path = path;
        }
    }

    return best_path;
}

int main() {
    cout << eval_time_path(generate_path()) << endl;
    return 0;
}