#include <bits/stdc++.h>

using namespace std;

ifstream fin("sate.in");
ofstream fout("sate.out");

const int MAX = 30005;
const int INF = 2e7+1;
int N, M, X, Y, d[MAX];
vector < pair <int, int> > A[MAX];
queue < pair <int, int> > q;
pair <int, int> sat, i;

void solve() {
    for(int i = 1; i <= N; ++i)
        d[i] = INF;
    d[X] = 0;
    q.push({X, 0});
    while(!q.empty()) {
        sat = q.front();
        q.pop();
        for(unsigned int j = 0; j < A[sat.first].size(); ++j) {
            i = A[sat.first][j];
            if(d[sat.first] + i.second < d[i.first])
               d[i.first] = d[sat.first] + i.second;
            if(i.first == Y) {
               fout << d[Y];
               return;
            }
            q.push({i.first, d[i.first]});
        }
    }
}


int main() {
    fin >> N >> M >> X >> Y;
    int a, b, d;
    while(M--) {
        fin >> a >> b >> d;
        A[a].push_back({b, d});
        A[b].push_back({a, -d});
    }
    solve();
}