#include <bits/stdc++.h>
using namespace std;
//ifstream in("sate.in");
//ofstream out("sate.out");

int n,m,i,j,x,y,a,b,c,X,Y;
vector <int> v[30010];
vector <int> d[30010];
bool viz[30010];
int dis[30010];


int main()
{
    ifstream cin("sate.in");
    ofstream cout("sate.out");
    cin>>n>>m>>x>>y;
    for(i=1;i<=m;i++)
    {
        cin>>a>>b>>c;
        v[a].push_back(b);
        v[b].push_back(a);
        d[a].push_back(c);
        d[b].push_back(c);
    }
    X=min(x,y);
    Y=max(y,x);
    dis[X]=0;
    queue <int> q;
    q.push(X);
    viz[X]=1;
    while(!dis[Y])
    {
        int curr=q.front();
        q.pop();
        for(int i=0;i<v[curr].size();i++)
            if(!viz[v[curr][i]])
                {
                    viz[v[curr][i]]=1;
                    q.push(v[curr][i]);
                    if (v[curr][i]<curr) dis[v[curr][i]]=dis[curr]-d[curr][i];
                    else dis[v[curr][i]]=dis[curr]+d[curr][i];
                }
    }


    cout<<dis[Y];

    return 0;
}