#include<iostream>
#include<fstream>
#include<stdio.h>
#include<bitset>
#include<queue>
#include<list>
using namespace std;
struct s
{
    int d;
    int l;
};
list<s> l[30002];
bitset<30002> v;
int calc(int x,int y)
{
    queue<s> q;
    q.push({x,0});
    s z;
    list<s>::iterator i;
    s a;
    while(q.size()>0)
    {
        z=q.front();
        q.pop();
        for(i=l[z.d].begin();i!=l[z.d].end();++i)
        {
            a=*i;
            if(a.d==y)
            {
                return z.l+a.l;
            }
            q.push({a.d,z.l+a.l});
        }
    }
}
int main()
{
    ifstream si;
    si.open("sate.in");
    FILE* so=fopen("sate.out","w");
    int n,m,x,y;
    si>>n>>m>>x>>y;
    --x;
    --y;
    int i,a,b,c;
    for(i=0;i<m;++i)
    {
        si>>a>>b>>c;
        --a;
        --b;
        l[a].push_back({b,c});
        l[b].push_back({a,-c});
    }
    fprintf(so,"%i\n",calc(x,y));
}