#include<bits/stdc++.h>
using namespace std;

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

int n,m,x2,y2,viz[3002],s=0;
vector< pair<int,int> >v[30002];
queue< int >q;

void bfs(int x)
{
    viz[x]=1;
    q.push(x);
    while(!q.empty())
    {
        int nod=q.front();
        q.pop();
        if(nod==y2)
            return;
        for(auto it:v[nod])
        {
            int nou=it.first;
            int cost=it.second;
            if(viz[nou]==0)
            {
                s+=cost;
                viz[nou]=1;
                q.push(nou);
            }
        }
    }
}

int 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<<s;
    return 0;
}