#include <bits/stdc++.h>

using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
vector<pair<int,int>>l[30005];
int n,m,x,y,xs,ys,c,sum,viz[30005];
void dfs(int nod)
{
    viz[nod]=1;
    if(nod==ys)
    {
        fout<<sum;
        exit(0);
    }
    for(auto next:l[nod])
    {
        if(!viz[next.first])
        {
            if(nod < next.first)
            {
                sum+=next.second;
            }
            else
                sum-=next.second;
            dfs(next.first);
        }
    }
}
int main()
{
   fin>>n>>m>>xs>>ys;
   for(int i=1;i<=m;i++)
   {
       fin>>x>>y>>c;
       l[x].push_back({y,c});
       l[y].push_back({x,c});
   }
   dfs(xs);
}