#include <bits/stdc++.h>
#define pii pair <int, int>
#define INF 0x3f3f3f3f

using namespace std;

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


struct str{
    int nod;
    int cost;
    bool operator <(const str&other)const
    {
        return cost>other.cost;
    }
};
priority_queue <str> pq;
vector <pii> v[30005];
int n,m,xx,yy,drum[30005];

void dijkstra()
{
    while(!pq.empty())
    {
        int nod=pq.top().nod;
        int cost=pq.top().cost;
        pq.pop();
        if(cost!=drum[nod])
            continue;
        for(auto it=v[nod].begin();it<v[nod].end();it++)
        {
            int nxt=(*it).first;
            int cst=(*it).second;
            if(drum[nod]+cst<drum[nxt])
            {
                drum[nxt]=drum[nod]+cst;
                pq.push({nxt,drum[nxt]});
            }
        }

    }
}

int main()
{
    fin>>n>>m>>xx>>yy;
    memset(drum,INF,sizeof(drum));
    for(int i=1;i<=m;i++)
    {
        int x,y,c;
        fin>>x>>y>>c;
        v[x].push_back({y,c});
        v[y].push_back({x,-c});
    }
    pq.push({xx,0});
    drum[xx]=0;
    dijkstra();
    fout<<drum[yy];
    return 0;
}