#include <fstream>
#include <vector>
#include <queue>

using namespace std;
const int NMAX = 30000;
const int INF = 21e8;

ifstream cin("sate.in");
ofstream cout("sate.out");

struct noduri {
    int nod, cost;
};
vector <vector <noduri>> v;

int dist[NMAX + 2], n;
bool f[NMAX + 2]; ///dc e in coada
void bfs(int start) {
    for(int i = 1; i <= n; i++)
        dist[i] = INF;
    dist[start] = 0;
    f[start] = 1;
    queue <int> q;
    q.push(start);

    while(!q.empty()) {
        int now = q.front();
        f[now] = 0;
        q.pop();
        for(auto var : v[now]) {
            if(dist[var.nod] > dist[now] + var.cost) {
                dist[var.nod] = dist[now] + var.cost;
                if(!f[var.nod]) {
                    f[var.nod] = 1;
                    q.push(var.nod);
                }
            }
        }
    }
}
int main()
{
    int m, x, y, a, b, c;
    cin >> n >> m >> x >> y;
    v.resize(n + 1);
    for(int i = 1; i <= m; i++) {
        cin >> a >> b >> c;
        if(a > b)
            swap(a, b);
        v[a].push_back({b, c});
        v[b].push_back({a, -c});
    }
    bfs(x);
    cout << dist[y];
    return 0;
}