#include <bits/stdc++.h>
#define DIM 30005
#define INF 1e9
using namespace std;
ifstream fin ("sate.in");
ofstream fout ("sate.out");

    vector<pair<int,int>>g[DIM];
    int d[DIM],v[DIM];
    int n,m,a,b,c,x,y;
    queue<int> q;
void bfs()
{
    for(int i=1;i<=n;++i)
        d[i]=INF;
    d[x]=0;
    q.push(x);v[x]=1;
    while(!q.empty())
    {
        int nod=q.front();
        q.pop();
        for(int i=0;i<g[nod].size();++i)
        {
           int vecin=g[nod][i].first;
           int cost=g[nod][i].second;
           if(vecin<nod&&v[vecin]==0)
            {
                d[vecin]=d[nod]-cost;
                if(vecin==y)
                {
                fout<<d[y];
                return;
                }
                q.push(vecin);
                v[vecin]=1;
            }
            else if(vecin>nod&&v[vecin]==0)
            {
                d[vecin]=d[nod]+cost;
                if(vecin==y)
                {
                    fout<<d[y];
                    return;
                }
                q.push(vecin);
                v[vecin]=1;
            }
        }
    }
    fout<<d[y]<<" ";
}

int main()
{
    fin >>n >>m >>x>>y;
    for(int i=1;i<=m;++i)
    {
        fin>>a>>b>>c;
        g[a].push_back(make_pair(b,c));
        g[b].push_back(make_pair(a,c));
    }
    bfs();

    return 0;
}