#include <bits/stdc++.h>
#define Nmax 30005
#define inf 1<<30

using namespace std;

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

int d[Nmax];

struct compara{
    bool operator()(int x,int y)
    {
        return d[x]>d[y];
    }
};

vector < pair<int,int> > mat[Nmax];
priority_queue<int, vector<int>, compara> coada;
int n,m,a,b,c,x,y;
bool incoada[Nmax];

void dijkstra(int nodstrat)
{
    for(int i=1;i<=n;i++)
        d[i]=inf;
    d[nodstrat]=0;
    coada.push(nodstrat);
    incoada[nodstrat]=1;
    while(!coada.empty())
    {
        int nod=coada.top();
        coada.pop();
        incoada[nod]=0;
        for(int i=0;i<mat[nod].size();i++)
        {
            int next=mat[nod][i].first;
            int cost=mat[nod][i].second;
            if(d[nod]+cost<d[next])
            {
                d[next]=d[nod]+cost;
                if(incoada[next]==0)
                {
                    coada.push(next);
                    incoada[next]=1;
                }
            }
        }
    }
}

int main()
{
    fin>>n>>m>>x>>y;
    for(int i=1;i<=m;i++)
    {
        fin>>a>>b>>c;
        mat[a].push_back({b,c});
        mat[b].push_back({a,-c});
    }
    dijkstra(x);
    fout<<d[y];
    return 0;
}