//#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]);
//                if(k<a[k][i]) s-=val[k][i];
//                else s+=val[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);
//    }
//    if(p>q) swap(p,q);
//    v[p]=1; t=true;
//    dfs(p);
//    g<<sm;
//    return 0;
//}


#include <vector>
#include <cstdio>

using namespace std;


int n,m,i,x,y,c,p,q,s,v[300001],sm,dist[300001];
bool t;
vector <int> a[300001],val[300001];
void dfs(int k){
    int i;

        for(i=0;i<a[k].size();++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];
                dist[a[k][i]]=s;
                dfs(a[k][i]);
                if(k<a[k][i]) s-=val[k][i];
                else s+=val[k][i];
            }
}
int main()
{
    freopen("sate.in", "r", stdin);
    freopen("sate.out", "w", stdout);

    scanf("%d%d%d%d",&n,&m,&p,&q);
    for(i=1;i<=n;++i){
        scanf("%d%d%d", &x, &y, &c);
        a[x].push_back(y); val[x].push_back(c);
        a[y].push_back(x); val[y].push_back(c);
    }
    //if(p>q) swap(p,q);
    v[p]=1;
    dfs(p);
    printf("%d",dist[q]);
    return 0;
}