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

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

vector < pair<int,int> > graph[30005];
queue <int> q;
int n,m,a,b,x,y,c,d[30005],i;
int main()
{
    f>>n>>m>>a>>b;
    while(m--)
    {
        f>>x>>y>>c;
        graph[x].push_back({y,c});
        graph[y].push_back({x,-c});
    }
    for(i=1;i<=n;i++)
    {
        d[i]=1e9;
    }
    if(a>b)
        swap(a,b);
    q.push(a);
    d[a]=0;
    while(!q.empty())
    {
        x=q.front();
        if(x==b)
        {
            g<<d[b];
            break;
        }
        q.pop();
        for(i=0;i<(int)graph[x].size();i++)
        {
            if(d[graph[x][i].first]>d[x]+graph[x][i].second)
            {
                d[graph[x][i].first]=d[x]+graph[x][i].second;
                q.push(graph[x][i].first);
            }
        }
    }
    return 0;
}