#include <iostream>
#include <stdio.h>
#include <vector>

using namespace std;

int nn,n,s,x,y,v[30100],i,j,k,a,b,u,p,l,nr;
vector<int> m[30100];
vector<int> cost[30100];
vector<int>::iterator it;
int d[2000100];

int main()
{

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

    scanf("%d %d %d %d",&n,&nn,&a, &b);

    for (i=1;i<=nn;i++)
    {
        scanf("%d %d %d",&x,&y,&l);
        //c[x]++;
        //m[(x-1)*100+c[x]]=y;
        m[x].push_back(y);
        cost[x].push_back(l);
        m[y].push_back(x);
        cost[y].push_back(l);
    }

    for (i=1;i<=n;i++)
    v[i]=-1;

    v[a]=0;

    p=0;u=1;d[1]=a;
    while (p<=u)
    {
        //d[p]=0;
        p++;

        //for (i=1;i<=m[x].size();i++)
        i=-1;
        for (it=m[d[p]].begin(); it<m[d[p]].end(); it++)
        {
            i++;
          //  printf("%d %d\n",cost[d[p]].at(i));
            nr=*it;
            if (v[nr]==-1)
            {
                u++;
                d[u]=nr;
                if (d[p]<nr)
                v[nr]=v[d[p]]+cost[d[p]].at(i);
                else
                v[nr]=v[d[p]]-cost[d[p]].at(i);
                if (nr==b) p=u+1;
            }
        }

    }


    //for (i=1;i<=n;i++)
    printf("%d ",v[b]);


    return 0;
}