#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;

ifstream in("sate.in");
ofstream out("sate.out");

int n,m,x,y;
vector < vector < pair < int, int > > > v;
vector < long long > cost;
vector < bool > inq;
queue < int > q;
const int INF = (1<<31)-1;

void init()
{
    v.resize(n+1);
    cost.resize(n+1,INF);
    inq.resize(n+1,false);
}

void citire()
{
    in>>n>>m>>x>>y;
    init();
    int i,a,b,c;
    for(i=1;i<=m;i++)
    {
        in>>a>>b>>c;
        v[a].push_back(make_pair(b,c));
        v[b].push_back(make_pair(a,-c));
    }
}

void rezolvare()
{
    int nod;
    vector < pair < int, int > >::iterator it;
    q.push(x);
    inq[x]=true;
    cost[x]=0;
    while(q.size())
    {
        nod=q.front();
        for(it=v[nod].begin();it!=v[nod].end();it++)
        {
            if(cost[it->first]>cost[nod]+it->second)
            {
                cost[it->first]=cost[nod]+it->second;
                if(!inq[it->first])
                    q.push(it->first);
            }
        }
        inq[nod]=false;
        q.pop();
    }
}

void afisare()
{
    out<<cost[y];
}

int main()
{
    citire();
    rezolvare();
    afisare();
    return 0;
}