#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
#define c1 second
#define n1 first

using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
const int inf = 0x3f3f3f3f;
queue <int > q;
vector < pair <int, int> >v[300000];
int sol[3000000],a,b,c,m,n,x,y;
void bfs(int s)
{
    q.push(s);
    for(int i=0; i<=n; i++)
    sol[i]=inf;
    sol[s]=0;
    while(!q.empty()||sol[y]==inf)
    {
        int curent=q.front();
        q.pop();
        for(int i=0; i<v[curent].size(); i++)
            if(sol[v[curent][i].n1]>sol[curent]+v[curent][i].c1)
            {
                q.push(v[curent][i].n1);
                sol[v[curent][i].n1]=sol[curent]+v[curent][i].c1;
            }
            }
    g<<sol[y];

}

int main()
{
    f>>n>>m>>x>>y;
    for(int i=1; i<=m; i++)
    {
        f>>a>>b>>c;
        v[a].push_back(make_pair(b,c));
        v[b].push_back(make_pair(a,-c));
    }
    bfs(x);
    return 0;
}