#include <fstream>
#include <vector>
#include <cstring>
#include <cmath>
#define DIM 30002
using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n,m,x,y,viz[DIM],C[DIM],D;
vector <int> v[DIM],d[DIM];
void BFS(int n){
    int p,u;
    viz[n]=0;
    C[1]=n;p=u=1;
    while(p<=u && viz[y]==-1){
        n=C[p++];
        for(int i=0;i<v[n].size();i++){
            if(viz[v[n][i]]==-1){
                if((n>x && v[n][i]>x && v[n][i]<n) || (n<x && v[n][i]<x && v[n][i]>n) || (n>x && v[n][i]<x) || (n<x && v[n][i]>x))
                    viz[v[n][i]]=abs(viz[n]-d[n][i]);
                else
                    viz[v[n][i]]=viz[n]+d[n][i];
                C[++u]=v[n][i];
            }
        }
    }
}
int main(){
    fin>>n>>m>>x>>y;
    while(m--){
        int g,f;
        fin>>g>>f>>D;
        v[g].push_back(f);
        v[f].push_back(g);
        d[g].push_back(D);
        d[f].push_back(D);
    }
    memset(viz,-1,sizeof(viz));
    BFS(x);
    fout<<viz[y];
    fin.close();fout.close();
    return 0;
}