#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
using namespace std;
ifstream in("sate.in");
ofstream out("sate.out");
struct tip{int j,d;};
queue <int>q;
int main()
{
    int n,m,i,x,y,s=0,au,b,d,u;
    in>>n>>m>>x>>y;
    x--;
    y--;
    vector<int>v[n];
    vector<struct tip>a[n];
    int c[n],pi[n];
    for(i=0;i<n;i++)
    {
        c[i] = false;
        pi[i]=0;
    }
    struct tip ele;
    for(i=0;i<m;i++)
    {
        in>>au>>b>>d;
        au--;
        b--;
        ele.j = b;
        ele.d=d;
        a[au].push_back(ele);
        ele.j=au;
        a[b].push_back(ele);
        v[au].push_back(b);
        v[b].push_back(au);
    }
    c[x] = true;
    q.push(x);
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        for(vector<int>::iterator it =v[u].begin();it!=v[u].end();++it)
            if (!c[*it])
        {
            c[*it]=true;
            q.push(*it);
            pi[*it] = u;
        }
    }
    int sup;
    struct tip z;
    bool ok = true;
    while(ok)
    {
        for(vector<struct tip>::iterator it=a[y].begin();it!=a[y].end();++it)
        {
             if ((*it).j==pi[y])
                {
                    sup = (*it).d;
                    continue;
                }
        }
        if (pi[y]<y)
            s = s+sup;
        else
            s=s- sup;
        y = pi[y];
        if (y == x)
            ok  = false;
    }
    out<<s;
    return 0;
}