#include <cstdio>
#include <vector>
#include <algorithm>
#define NMax 30000
#define oo 1<<30
#define x first
#define y second
using namespace std;

typedef pair<int, int> abc;
vector<abc> a[NMax+1];
int COADA[NMax+1];
int v[NMax+1];

void BFS(int X)
{
    int inc,sf,i,k,idx;

    inc = sf = v[X] = 0;
    COADA[0] = X;
    while(inc <= sf)
    {
        k = COADA[inc++];
        for(i = 0; i < a[k].size(); ++i)
        {
            idx = a[k][i].x;
            if( v[idx] == oo )
            {
                COADA[++sf] = idx;
                v[idx] = v[k] + a[k][i].y;
            }
        }
    }
}

int main(){
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);

    int i,N,M,X,Y,x,y,d;

    scanf("%d %d %d %d",&N,&M,&X,&Y);
    if(X > Y) swap(X,Y);
    for(i = 1; i <= M; ++i)
    {
        scanf("%d %d %d",&x,&y,&d);
        a[x].push_back({y,d});
        a[y].push_back({x,-d});
    }

    for(i = 1; i <= N; ++i) v[i] = oo;
    BFS(X);
    printf("%d\n",v[Y]);


return 0;
}