#include <iostream>
#include<fstream>
#include<queue>
#include<algorithm>
#include<vector>
#define vecin first
#define dist second
using namespace std;

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

const int nmax = 30005;
const int mmax = 100050;
int n, m, x, y, d[nmax];
vector<pair<int, int> > graf[nmax];
queue<int> q;

int BFS_x_to_y(int start, int finnish ){

    int nod_curent;
    q.push(start);
    d[start] = 0;

    while(!q.empty()){
        nod_curent = q.front();
        q.pop();

        if(nod_curent == finnish){
            return d[finnish];
        }

        for(int i = 0; i < graf[nod_curent].size(); ++i){
            int v = graf[nod_curent][i].vecin;
            int k = graf[nod_curent][i].dist;
            if(d[v] == 0 && v != 1){
                q.push(v);
                if( v < nod_curent ) d[v] = d[nod_curent] - k;
                else d[v] = d[nod_curent] + k;
            }
        }
    }
}

int main()
{

    in >> n >> m >> x >> y;
    for(int i = 1; i <= m; ++i){
        int a, b, c; in >> a >> b >> c;
        graf[a].push_back( make_pair(b, c) );
        graf[b].push_back( make_pair(a, c) );
    }

    out<<BFS_x_to_y(x, y);

    in.close();
    out.close();
    return 0;
}