#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
long long s=0,n,m,x,y,i,nr,maxi=-609,benis,a,b,b1,b2,visitat[100001];
struct pc
{
    int nod;
    long long dist;
} cd;
vector<pc>v[100001];
vector<int>bn;
void filix(int x,int dest,int nmr)
{
visitat[x]=1;
if(x==dest)
    s=nmr;
for(i=0;i<v[x].size();i++)
{
    if(visitat[v[x][i].nod]==0)
    {
        nmr+=v[x][i].dist;
        filix(v[x][i].nod,dest,nmr);
    nmr-=v[x][i].dist;
    }
}
}

int main()
{
    ifstream in("sate.in");
    ofstream out("sate.out");
    in>>n>>m>>x>>y;
    for(i=1; i<=m; i++)
    {
        in>>a>>b>>nr;
        cd.nod=a;
        cd.dist=-nr;
        v[b].push_back(cd);
        cd.nod=b;
        cd.dist=nr;
        v[a].push_back(cd);
    }
    filix(x,y,0);
out<<s<<' ';

    return 0;
}
//adiacenta