#include <bits/stdc++.h>
using namespace std;
int n,m,i,j,k,ans,x,y;
vector<pair<int,int>>g[30005];
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>pq;
queue<int>q;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    freopen("sate.in", "r", stdin);
    freopen("sate.out", "w", stdout);
    cin>>n>>m>>x>>y;
    while (m--)
    {
        int d;
        cin>>i>>j>>d;
        g[i].push_back({d,j});
        g[j].push_back({d,i});
    }
    vector<int>dist(n+1,INT_MAX);
    vector<bool>seen(n+1,false);
    seen[x]=true;
    dist[x]=0;
    q.push(x);
    while (!q.empty())
    {
        int u=q.front();
        q.pop();
        for (auto v : g[u])
        {
            if (!seen[v.second])
            {
                seen[v.second]=true;
                if (u<v.second)
                {
                    dist[v.second]=dist[u]+v.first;
                }
                else
                {
                    dist[v.second]=dist[u]-v.first;
                }
                q.push(v.second);
            }
        }
    }
    cout<<abs(dist[y]);
}