#include <cstdio>
#include<vector>
using namespace std;
vector<int> v[30001],c[30001];
int q[30001],p,u;
int n,m,x,y,a,b,i,fix,cost[30001],dist,s;
int main()
{
    freopen("sate.in","r",stdin);
    freopen("sate.out","w",stdout);
    scanf("%d%d%d%d",&n,&m,&x,&y);
    for(i=1;i<=m;i++)
    {
        scanf("%d%d%d",&a,&b,&dist);
        if(b<a) swap(a,b);
        v[a].push_back(b);
        v[b].push_back(a);
        c[b].push_back(dist);
        dist*=-1;
        c[a].push_back(dist);

    }
    cost[x]=0;
    p=1;
    u=1;
    q[p]=x;
    while(p<=u&&cost[y]==-1)
    {
        s=q[p];
        p++;
        fix=v[s].size();
        for(i=0;i<fix;i++)
        {
            if(cost[v[s][i]]==0&&v[s][i]!=x)
            {cost[v[s][i]]=cost[s]+c[s][i];
            u++;q[u]=v[s][i];if(v[s][i]==y)break;}
        }
    }
    if(cost[y]<0) cost[y]*=-1;
    printf("%d",cost[y]);

    return 0;
}