#include <iostream>
#include <fstream>
#include <queue>
#define NMAX 30000

using namespace std;

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

int n, m, x, y, dist[NMAX+10];
bool viz[NMAX+10];
vector <pair <int, int> > nod[NMAX+10];
queue <int> Q;

void bfs(int val)
{   viz[val] = 1;
    Q.push(val);
    while(!Q.empty())
        {   val = Q.front();
            Q.pop();

            if(val == y) return;
            for(int i=0; i<nod[val].size(); i++)
                if(!viz[nod[val][i].second])
                    {   dist[nod[val][i].second] = dist[val] + nod[val][i].first;
                        viz[nod[val][i].second] = 1;
                        Q.push(nod[val][i].second);
                    }
        }
}

int main()
{
    ifstream cin("sate.in");
    ofstream cout("sate.out");
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n >> m >> x >> y;
    if(x > y) swap(x, y);
    for(int i=1; i<=m; i++)
        {   int nod1, nod2, cost;
            cin >> nod1 >> nod2 >> cost;
            if(nod1 > nod2) swap(nod1, nod2);
            nod[nod1].push_back(make_pair(cost, nod2));
            nod[nod2].push_back(make_pair(-cost, nod1));
        }
    bfs(x);
    cout << dist[y] << '\n';
    return 0;
}