#include <bits/stdc++.h>

using namespace std;
ifstream in("sate.in");
ofstream out("sate.out");
int n,m,x,y,c,d[30005],vis[30005],a,b;
vector<pair<int,int>> v[30005];
queue<int> q;
void bfs(int nod)
{
    q.push(nod);
    while(!q.empty())
    {
        x=q.front();
        vis[x]=1;
        q.pop();
        for(auto it:v[x])
        {
            if(vis[it.second]==0)
           {
            if(it.second>x) d[it.second]=d[x]+it.first;
            else d[it.second]=d[x]-it.first;
            if(it.second==b)
            {
                out<<abs(d[it.second]);
                return ;
            }
            q.push(it.second);
           }
        }
    }
}
int main()
{
    in>>n>>m>>a>>b;
    for(int i=1;i<=n;i++)
    {
        in>>x>>y>>c;
        v[x].push_back({c,y});
        v[y].push_back({c,x});
    }
    bfs(a);
    return 0;
}