#include <bits/stdc++.h>

using namespace std;

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

int n,m,x,y;
bool gy;
vector<vector<pair<int,int>>>a;
vector<bool> viz;

void bfs(int st) {
    queue<pair<int,int>>q;
    q.push({st,0});
    while (!q.empty()) {
        int nod=q.front().first,dist=q.front().second;
        q.pop();
        if (nod==y) {
            gy=true;
            fout<<dist;
        }
        for (auto f:a[nod]) {
            if (!viz[f.first]) {
                if (f.first>nod) q.push({f.first,dist+f.second});
                else q.push({f.first,dist-f.second});
                viz[f.first]=true;
            }
        }
    }
}

int main() {
    fin>>n>>m>>x>>y;
    a.resize(n+1);
    viz.resize(n+1);
    int na,nb,nc;
    for (int i=1;i<=n;i++) {
        fin>>na>>nb>>nc;
        a[na].push_back({nb,nc});
        a[nb].push_back({na,nc});
    }
    bfs(x);
    if (!gy) fout<<"-1";
    return 0;
}