#include <iostream>
#include <cstring>

using namespace std;

const int C = 6210;
const int T = 2510;
int m, t, b, e;
int g[T][T];
int dist[T];
bool st[T];

void dijkstra() {
    memset(dist, 0x3f, sizeof dist);
    memset(st, 0, sizeof st);
    dist[b] = 0;
    for (int i = 1 ; i <= t; i ++) {
        int j = -1;
        for (int k = 1; k <= t ;k ++) {
            if(!st[k] && (j == -1 || dist[j] > dist[k])){
                j = k;
            }
        }
        st[j] = true;
        for (int k = 1; k <= t ; k ++) {
            dist[k] = min(dist[k], dist[j] + g[k][j]);
        }
    }
}

int main() {
    cin >> t >> m >> b >> e;
    memset(g, 0x3f, sizeof g);
    for (int i = 1 ; i <= m ; i ++) {
        int a, b, c;
        cin >> a >> b >> c;
        g[a][b] = g[b][a] = min(g[a][b], c);
    }
    dijkstra();
    cout << dist[e] << endl;
    return 0;
}