#include <bits/stdc++.h>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,i,x,y,c,p,q,s,v[30001],sm;
bool t;
vector <int> a[30001],val[30001];
void dfs(int k){
    int i;
    if(k==q){ t=false; sm=s; }
    else{
        for(i=0;i<a[k].size() && t;++i)
            if(v[a[k][i]]==0){
                v[a[k][i]]=1;
                if(k<a[k][i]) s+=val[k][i];
                else s-=val[k][i];
                dfs(a[k][i]);
            }
    }
}
int main()
{
    f>>n>>m>>p>>q;
    for(i=1;i<=n;++i){
        f>>x>>y>>c;
        a[x].push_back(y); val[x].push_back(c);
        a[y].push_back(x); val[y].push_back(c);
    }
    v[p]=1; t=true;
    dfs(p);
    g<<sm;
    return 0;
}