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

using namespace std;

int nn,n,s,x,y,v[100100],i,j,k,a,b,u,p,c[100100],l;
vector<int> m[100100],cost[100100];
vector<int>::iterator it,r;
int d[1000100];

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);
    }

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

    v[s]=0;

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

        //for (i=1;i<=m[x].size();i++)
        i=0;
        for (it=m[d[p]].begin(); it<m[d[p]].end(); it++)
        {
            i++;
            //printf("%d \n",*it);
            if (v[*it]==-1)
            {
                u++;
                d[u]=*it;
                if (d[p]<*it)
                v[*it]=v[d[p]]+cost[d[p]].at(i);
                else
                v[*it]=v[d[p]]-cost[d[p]].at(i);
            }
        }

    }


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


    return 0;
}