#include<fstream>
#include<vector>
#include<queue>
#include<cstring>
#define max(a,b) (a>b?a:b)
#define min(a,b) (a<b?a:b)
using namespace std;
ifstream in("sate.in");
ofstream out("sate.out");
const int Nmax = 30002;
vector<int> G[Nmax],C[Nmax];
int D[Nmax],Piv[Nmax];
queue<int> q;
int inq[Nmax];
int N,M,X,Y;
int main(){
    in>>N>>M>>X>>Y;
    for(int i=1;i<=M;i++){
        int x,y,c;
        in>>x>>y>>c;
        G[x].push_back(y);
        G[y].push_back(x);
        C[x].push_back(c);
        C[y].push_back(c);
    }
    memset(D,-1,sizeof(D));
    int i=1;
    while( D[X]==-1 || D[Y]==-1 || i<=N){
        if( D[i]==-1 ){
            D[i]=0;
            Piv[i]=i;
            q.push(i);
            inq[i]=1;
            while(!q.empty()){
                int p=q.front();
                q.pop();
                inq[p]=0;
                for(int j=0;j<G[p].size();j++){
                    if( D[ G[p][j] ]==-1 ){
                        if( G[p][j] < p ){
                            D[ G[p][j] ] = D[p] - C[p][j];
                        }
                        else{
                            D[ G[p][j] ] = D[p] + C[p][j];
                        }
                        Piv[ G[p][j] ] = Piv[p];
                        if( !inq[ G[p][j] ] ){
                            q.push(G[p][j]);
                            inq[G[p][j]]=1;
                        }
                    }
                }
            }
        }
        i++;
    }
    out<< D[max(X,Y)] - D[min(X,Y)] ;
    return 0;
}