#include<iostream>
#include<fstream>
using namespace std;
ifstream in("sate.in");
ofstream out("sate.out");
int mat[5000][5000],n,m,inceput,sfarsit,i,j,k,p,viz[5000],coada[5000],cost[5000];
void citire()
{
    in>>n>>m>>inceput>>sfarsit;
      int a,b,c;
    for(i=1;i<=n;i++)
    for(j=1;j<=n;j++)
    if(i!=j)
    mat[i][j]=99999;
    else
    mat[i][j]=0;
    for(i=1;i<=m;i++)
    {in>>a>>b>>c;
     mat[a][b]=mat[b][a]=c;
    }
}
int dfs()
{viz[inceput]=1;
coada[1]=inceput;
p=1;
int ok;
while(coada[p]!=sfarsit)
{
ok=0;
for(i=1;i<=n;i++)
if(viz[i]!=1&&mat[coada[p]][i]!=99999)
{viz[i]=1;
p++;
coada[p]=i;
ok=1;
if(coada[p-1]<i)
{cost[p]=cost[p-1]+mat[coada[p-1]][i];}
else
{cost[p]=cost[p-1]-mat[coada[p-1]][i];}
}
if(ok==0)
{p--;
}
}//for(i=1;i<=n;i++)
///cout<<cost[i]<<" ";
out<<cost[p];
}
int main()
{citire();
dfs();
}