#include <iostream>
#include <vector>
#include <queue>
#include <cstdio>
#define M 100056
#define MAXBUF (1<<20)
FILE*fi,*fout;
using namespace std;


vector <int> A[M];
vector <long> cost[M];
queue<int> coada;
int n,m,i,j,x,y,el,G[M];
bool viz[M];
long costf[M];

char buf[MAXBUF];
int pos=MAXBUF;
inline char nextch(){
    if(pos==MAXBUF){
       fread(buf,1,MAXBUF,fi);
       pos=0;
    }
    return buf[pos++];
}
inline int getnr(){
   char a=nextch();
   while(a<'0'||a>'9')
      a=nextch();
   int nr=0;
   while(a>='0'&&a<='9'){
      nr=nr*10+a-'0';
      a=nextch();
   }
   return nr;
}
inline void lee(int x)
{
    coada.push(x);
    viz[x]=1;
    while(!coada.empty())
    {
        el=coada.front();
        coada.pop();
        for(int k=0;k<A[el].size();k++)
        {
            if(viz[A[el][k]]==0)
            {
                costf[A[el][k]]=costf[A[el][k]]+costf[el]+cost[el][k];
                if(A[el][k]==y)
                    return;
                coada.push(A[el][k]);
                viz[A[el][k]]=1;
            }
        }
    }
}
int main()
{
    int x1,y1,cos;
    fi=fopen("sate.in","r");
    fout=fopen("sate.out","w");
    n=getnr();
    m=getnr();
    x=getnr();
    y=getnr();
    while(m!=0)
    {
        x1=getnr();
        y1=getnr();
        cos=getnr();
        A[x1].push_back(y1);
        A[y1].push_back(x1);
        cost[x1].push_back(cos);
        cost[y1].push_back((-1)*cos);
        m--;
    }
    lee(x);
    fprintf(fout,"%d",costf[y]);
    return 0;
}