#include <bitset>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#define NMAX 200001
#define MAX 150001
#define pb push_back
#define MOD 1000000007
#define nl '\n'
#define INF 0x3f3f3f3f
#define pii1 pair<int, pair<int,int>>  (1,(1,2));
#define pii pair<int,int>
#define tpl tuple<int,int,int>
#define int long long
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
int n,m,x,y,ans,X,Y;
vector<vector<pii>>G(NMAX);
vector<int>dist(NMAX);
void dijkstra(int node)
{
    priority_queue<pii,vector<pii>,greater<pii>>pq;
    for(int i=1;i<=n;++i)
        dist[i]=INF;

    dist[node]=0;
    pq.push({0,node});
    while(!pq.empty())
    {
        auto [dis,first]=pq.top();
        pq.pop();
        for(auto [u,w]:G[first])
        {
            if(dist[u]>dist[first]+w)
            {
                dist[u]=dist[first]+w;
                pq.push({dist[u],u});
            }
        }
    }
}
signed main() {

    fin>>n>>m>>X>>Y;
    for(int i=1;i<=m;++i)
    {
        int c;
        fin>>x>>y>>c;
        G[x].pb({y,c});
        G[y].pb({x,-c});
    }
    dijkstra(X);
    fout<<dist[Y];




    return 0;
}