#include <cstdio>
#include <vector>
#include <cstring>
#include <cmath>
#define DIM 30002
#define a first
#define b second
using namespace std;

int n,m,x,y,viz[DIM],C[DIM],D,dist[DIM];
vector < pair<int,int> > v[DIM];
void BFS(int n){
    int p,u;
    viz[n]=1;
    C[1]=n;p=u=1;
    while(p<=u && !viz[y]){
        n=C[p++];
        for(int i=0;i<v[n].size();i++){
            if(!viz[v[n][i].a]){
                if((n>x && v[n][i].a>x && v[n][i].a<n) || (n<x && v[n][i].a<x && v[n][i].a>n) || (n>x && v[n][i].a<x) || (n<x && v[n][i].a>x))
                    dist[v[n][i].a]=abs(dist[n]-v[n][i].b);
                else
                    dist[v[n][i].a]=dist[n]+v[n][i].b;
                viz[v[n][i].a]=1;
                C[++u]=v[n][i].a;
            }
        }
    }
}
int main(){
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&x,&y);
    while(m--){
        int g,f;
        scanf("%d%d%d",&g,&f,&D);
        v[g].push_back(make_pair(f,D));
        v[f].push_back(make_pair(g,D));
    }
    BFS(x);
    printf("%d",dist[y]);
    return 0;
}