#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

ifstream fin("sate.in");
ofstream fout("sate.out");

vector <int> v[300005];
vector <int> d[300005];

int n,m,q[300006],a,b,ls,ld,pred[300006];
bool bgr[300006];

void drum(){
    int r=0;
    while(b!=a){
        for(int i=0;i<v[pred[b]].size();i++){
            if(v[pred[b]][i]==b){
                r+=d[pred[b]][i];
            }
        }
        b=pred[b];
    }
    fout<<r;
    return;
}

void bfs(){
    int cld=ld;
    for(int i=ls;i<=cld;i++){
        int nc=q[i];
        bgr[nc]=true;
        if(nc==b){
            drum();
            return;
        }
        for(int ii=0;ii<v[nc].size();ii++){
            if(!bgr[v[nc][ii]]){
                ld++;
                q[ld]=v[nc][ii];
                pred[v[nc][ii]]=nc;
            }
        }
    }
    ls=cld+1;
    bfs();
}

int main()
{
    int x,y,dax;
    fin>>n>>m>>a>>b;
    for(int i=0;i<m;i++){
        fin>>x>>y>>dax;
        d[x].push_back(dax);
        d[y].push_back(-dax);
        v[x].push_back(y);
        v[y].push_back(x);
    }
    q[0]=a;
    bfs();
    return 0;
}