#include <fstream>
#include <queue>
#include <vector>
#define NMAX 30002
using namespace std;

int n, m;
int x, y;
int dist;
queue<int> q;
queue<int> d;
vector<int> v[NMAX];
vector<int> c[NMAX];
char viz[NMAX];


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

void read() {
    in>>n>>m>>x>>y;
    int a, b, cost;
    if (x > y) swap(x, y);

    for (int i = 1; i <= m; i++) {
        in>>a>>b>>cost;
        v[a].push_back(b);
        c[a].push_back(cost);
        v[b].push_back(a);
        c[b].push_back(cost);
    }
}

void bfs() {
    q.push(x);
    d.push(0);
    viz[x] = 1;
    int sat, lim, vecin;
    while (!q.empty()) {
        sat = q.front();
        dist = d.front();
        if (sat == y)
            break;
        q.pop();
        d.pop();
        lim =  v[sat].size();
        for (int i = 0; i < lim; i++) {
             vecin = v[sat][i];
            if (!viz[vecin]) {
                viz[vecin] = 1;
                q.push(vecin);
                if (vecin > sat) {
                    d.push(dist + c[sat][i]);
                } else {
                    d.push(dist - c[sat][i]);
                }
            }
        }
    }
}

int main() {
    read();
    bfs();
    out<<dist;
    return 0;
}