#include <bits/stdc++.h>
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
int n, i, j, c, dist[100005];
vector <pair <int, int>> mat[100005];
queue<int> q;
void bfs(int node)
{
    for(int a=0;a<=n; a++)
        dist[a]=1e9;
    dist[node]=0;
    q.push(node);
    while(!q.empty())
    {
        node=q.front();
        q.pop();
        for (auto x : mat[node]) {
            int a = x.first;
            int c = x.second;
            if(dist[node]+c<dist[a])
            {
                dist[a]=dist[node]+c;
                q.push(a);
            }
        }
    }
}
int main()
{
    int x,y,m;
    fin>>n>>m>>x>>y;
    while(fin>>i>>j>>c)
    {
        if (i > j) swap(i,j);
        mat[i].push_back({j,c});
        mat[j].push_back({i, -c}); //satele sunt de la st la dr; daca ma intorc, merg negativ!!
    }
    bfs(x);
    fout<<dist[y];
}