/* [A][M][C][B][N] / [K][R][I][P][6][8] */
#include <bits/stdc++.h>
using namespace std;
const char sp = ' ', nl = '\n';
const int MOD = 1000000007;
ifstream fin("sate.in");
ofstream fout("sate.out");

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int n, m, x, y;
    fin >> n >> m >> x >> y;
    if (x > y) x ^= y ^= x ^= y;
    vector<vector<pair<int, int>>> edgeList(n + 1);
    for (int q = 0; q < m; ++q) {
        int i, j, d;
        fin >> i >> j >> d;
        if (i > j) i ^= j ^= i ^= j;
        edgeList[i].push_back(make_pair(j, d));
        edgeList[j].push_back(make_pair(i, -d));
    }
    edgeList[y].push_back(make_pair(0, 0));
    queue<pair<int, int>> q;
    q.push(make_pair(x, 0));
    int cur_idx, cur_dist;
    while (!q.empty()) {
        if (!q.front().first) {
            fout << q.front().second;
            return 0;
        }
        cur_idx = q.front().first, cur_dist = q.front().second, q.pop();
        if (edgeList[cur_idx].empty()) continue;
        for (const pair<int, int>& pr : edgeList[cur_idx]) {
            q.push(make_pair(pr.first, cur_dist + pr.second));
        }
        edgeList[cur_idx].clear();
    }
    fout << -1;
}