#include <iostream>
#include<fstream>
#include<vector>
#include<deque>

using namespace std;
vector<int> v[30005],c[30005];
int q[30005],p,u;
int n,m,x,y,a,b,i,ge[30005],cost[30005],dist,s;
int main()
{
    freopen("sate.in","r",stdin);
    ofstream g("sate.out");
    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);

    }


    for(i=1;i<=n;i++) {cost[i]=-1;
    ge[i]=v[i].size();}
    cost[x]=0;
    p=1;
    u=1;
    q[p]=x;
    while(p<=u&&cost[y]==-1)
    {
        s=q[p];
        p++;
        for(i=0;i<ge[s];i++)
        {
            if(cost[v[s][i]]==-1)
            {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;
    g<<cost[y];

    return 0;
}