#include <iostream>
#include<fstream>
#include<vector>
#include<fstream>
#include<algorithm>
#include<cmath>
#define Nmax 20000002
typedef int coada[30001];
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int a,p,cst[30001],n,m,x,y,i,j,cost,q,k,l,nod,ultim;
coada c;
bool ok;
vector<pair <int,int> >v[30001];
inline void BFS(int nod)
{
    int k,l,n1=n*n;
    cst[nod]=0;
    int siz=1,start=1;
    c[start]=nod;
    while(siz>=start)
    {
        k=c[start];
        for(int i=0;i<v[k].size();i++)
            {
                l=v[k][i].first;
                {
                    if(cst[l]>cst[k]+v[k][i].second)
                    {
                        cst[l]=cst[k]+v[k][i].second;
                        c[++siz]=l;
                    }
                }
            }
        start++;
    }
}
int main()
{
    f>>n>>m>>x>>y;
    for(q=1;q<=m;q++)
    {
        f>>i>>j>>cost;
        if(i>j)
            swap(i,j);
        v[i].push_back(make_pair(j,cost));
        v[j].push_back(make_pair(i,-cost));
    }
    for(i=1;i<=n;i++)
        cst[i]=Nmax;
    BFS(x);
    g<<cst[y];
    return 0;
}