B

#include <bits/stdc++.h>

using namespace std;

const int N = (int) 5e1;
const int inf = (int) 1e9;

struct Matrix {
    vector<vector<int>> mat;

    Matrix() {

    }

    Matrix(int n) {
        mat = vector<vector<int>>(n, vector<int>(n, inf));
    }

    Matrix(vector<vector<int>> _mat) {
        mat = _mat;
    }

    void print() {
        int n = mat.size();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                printf("%d%c", mat[i][j], " \n"[j + 1 == n]);
            }
        }
    }

    friend Matrix operator * (Matrix a, Matrix b) { // a, b - square matrices
        int n = a.mat.size();
        Matrix c = Matrix(n);

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                for (int k = 0; k < n; k++) {
                    if (a.mat[i][k] == inf || b.mat[k][j] == inf) {
                        continue;
                    }

                    int v = a.mat[i][k] + b.mat[k][j];

                    if (k == 0) {
                        c.mat[i][j] = v;
                    } else {
                        c.mat[i][j] = min(c.mat[i][j], v);
                    }
                }
            }
        }

        return c;
    }

    friend void operator *= (Matrix &a, Matrix b) {
        a = a * b;
    }

    void operator = (Matrix b) {
        mat = b.mat;
    }
} g;

int n;

bool vis[N];

void dfs(int v) {
    for (int i = 0; i < n; i++) {
        if (!vis[i] && g.mat[v][i] != inf) {
            vis[i] = true;
            dfs(i);
        }
    }
}

Matrix bin_pow(Matrix a, int n) {
    Matrix r = a;
    --n;
    while (n > 0) {
        if (n & 1) {
            if (r.mat.empty()) {
                r = a;
            } else {
                r *= a;
            }
        }
        a *= a;
        n >>= 1;
    }
    return r;
}

int main() {
    int m, s, t;
    cin >> n >> m >> s >> t;
    --s;
    --t;

    g = Matrix(n);

    for (int i = 0; i < m; i++) {
        int x, y, l;
        cin >> x >> y >> l;
        --x;
        --y;
        g.mat[x][y] = min(g.mat[x][y], l);
        g.mat[y][x] = min(g.mat[y][x], l);
    }

    dfs(s);

    if (vis[s] && vis[t]) {
        Matrix res = bin_pow(g, 2018);

        while (true) {
            if (res.mat[s][t] != inf) {
                cout << res.mat[s][t] << "\n";
                break;
            } else {
                res *= res;
                res *= g;
            }
        }
    } else {
        puts("Mumkun emes");
    }
}