///#include <iostream>
#include <fstream>
#include <deque>
#include <map>
#include <vector>
const int SIZE = 32e3;

using namespace std;
typedef pair<int,int> pii;

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

void readit();
void BFS();
void coutVec();

int n, m, start, fin;
map <int, int> v[SIZE];

int main()
{
    readit();
    BFS();
    cout<<v[start][fin];
    return 0;
}

void readit()
{
    int y, x, c;
    cin>>n>>m>>start>>fin;
    for(int i=1; i<=m; i++)
        cin>>y>>x>>c,
        v[y][x]= c,
        v[x][y]=-c;
}

void coutVec()
{
    for(int i=1; i<=n; i++)
    {
        cout<<i<<": \n";
        for(auto el : v[i])
            cout<<"\t"<<el.first<<" = "<<el.second<<"\n";
    }
}

void BFS()
{
    pii now;
    deque <pii> bfsq;
    for(auto el : v[start])
        bfsq.push_back({start, el.first});
    while(!bfsq.empty())
    {
        now=bfsq.front();
        bfsq.pop_front();
        for(auto nxt : v[now.second])
            if(!v[now.first][nxt.first] && now.first!=nxt.first)
        {
            v[now.first][nxt.first]=v[now.first][now.second]+v[now.second][nxt.first];
            v[nxt.first][now.first]=-v[now.first][nxt.first];
            bfsq.push_back({now.first, nxt.first});
        }
    }
}