#include <iostream>
#include <fstream>
#include <vector>
#include <queue>

using namespace std;

vector<pair<int,long long> >g[30003];
int x,y,m,n,sol;
long long d[30003];
queue<int>q;

void citire()
{
    ifstream fin("sate.in");
    fin>>n>>m>>x>>y;
    if(x>y)
    {
        int aux;
        aux=x;
        x=y;
        y=aux;
    }
    int a,b,c;
    for(int i=0;i<m;i++)
    {
        fin>>a>>b>>c;
        g[a].push_back(make_pair(b,c));
        g[b].push_back(make_pair(a,c));
    }
}

void bfs()
{
    q.push(x);
    int c;
    while(!q.empty())
    {
        c=q.front();
        q.pop();
        for(auto&v:g[c])
        {
            if(d[v.first]==0)
            {
                q.push(v.first);
                if(c<v.first)
                    d[v.first]=d[c]+v.second;
                else
                    d[v.first]=d[c]-v.second;
                if(v.first==y)
                    return;
            }
        }
    }
}

void afisare()
{
    ofstream fout("sate.out");
    if(d[y]<0)
        d[y]=-d[y];
    fout<<d[y];
}

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