#include <bits/stdc++.h>
using namespace std;
const int NMAX = 3e5+2;
int n,m,x,y,a,b,c,d[NMAX],vf[NMAX];
vector<pair<int, int>> v[NMAX];

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

void dfs(int nod){
    vf[nod] = 1;
    for(auto [vecin, cost]: v[nod]){
        if(vf[vecin]){
            continue;
        }
        d[vecin] = d[nod]+cost;
        dfs(vecin);
    }
}

int main()
{
    fin >> n >> m >> x >> y;
    if(x > y){
        swap(x, y);
    }
    for(int i = 1; i <= m; i++){
        fin >> a >> b >> c;
        v[a].push_back({b, c});
        v[b].push_back({a, -c});
    }
    dfs(x);
    fout << d[y];
    return 0;
}