#include<bits/stdc++.h>
#define int long long
#define INF 2000000000
using namespace std;

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

int n,m,x2,y2,d[30002],viz[30002];
vector< pair<int,int> >v[30002];
queue< int >q;

void bfs(int x)
{
    int i;
    for(i=1; i<=n; i++)
        d[i]=INF;
    q.push(x);
    d[x]=0;
    viz[x]=1;
    while(!q.empty())
    {
        int nod=q.front();
        q.pop();
        for(auto it:v[nod])
        {
            if(viz[it.first]==0)
            {
                viz[it.first]=1;
                int nou=it.first;
                int cost=it.second;
                if(d[nou]>d[nod]+cost)
                {
                    d[nou]=d[nod]+cost;
                    q.push(nou);
                }
            }
        }
    }
}

signed main()
{
    int i,x,y,c;
    f>>n>>m>>x2>>y2;
    for(i=1; i<=m; i++)
    {
        f>>x>>y>>c;
        v[x].push_back(make_pair(y,c));
        v[y].push_back(make_pair(x,-c));
    }
    bfs(x2);
    g<<d[y2];
    return 0;
}