#include <bits/stdc++.h>
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
int n, i, j, c, mat[305][305], dist[305];
queue<int> q;
void bfs(int node)
{
    for(int a=0;a<=n; a++)
        dist[a]=1e6;
    dist[node]=0;
    q.push(node);
    while(!q.empty())
    {
        node=q.front();
        q.pop();
        for(int a=1; a<=n; a++)
        {
            if(mat[node][a])
            {
                if(dist[node]+mat[node][a]<dist[a])
                {
                    dist[a]=dist[node]+mat[node][a];
                    q.push(a);
                }
                else{dist[a]=dist[node]-mat[node][a];}
            }
        }
    }
}
int main()
{
    int x,y,m;
    fin>>n>>m>>x>>y;
    while(fin>>i>>j>>c)
    {
        mat[i][j]=c;
        mat[j][i]=-c; //satele sunt de la st la dr; daca ma intorc, merg negativ!!
    }
    bfs(x);
    fout<<dist[y];
}