#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <cmath>
#define inf 1000000001

using namespace std;

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

int n,m,p,s;

vector<vector<pair<int,int> > > v;
vector<int> dr;

void citire()
{
    f>>n>>m>>p>>s;
    v=vector<vector<pair<int,int> > > (n+1);
    dr=vector<int>(n+1);
    for(int i=1; i<=m; i++)
    {
        int a,b,c;
        f>>a>>b>>c;
        v[a].push_back(make_pair(b,c));
        v[b].push_back(make_pair(a,c));
    }
}

void rezolvare()
{
    int pre=p;
    queue<int>h;
    int ok=1;
    h.push(p);
    while(!h.empty())
    {
        int r=h.front();
        pre=r;
        h.pop();
        for(vector<pair<int,int> >::iterator it=v[r].begin(); it!=v[r].end(); it++)
        {
            int q=it->first;
            int w=it->second;
            if(dr[q]==0)
            {
                if(q>p)
                {
                    if(q<pre) dr[q]=dr[pre]-w;
                    else dr[q]=dr[pre]+w;
                }
                else
                {
                    dr[q]=dr[pre]-w;
                }
                h.push(q);
            }
            if(q==s) ok=0;
        }
        if(ok==0) break;
    }
}

int main()
{
    citire();
    rezolvare();
    g<<abs(dr[s]);
    return 0;
}