#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
using namespace std;
ifstream in ("sate.in");
ofstream out("sate.out");
long const N=30001;
unsigned n,m,x,y;
bool viz[N];
unsigned long cost[N];
vector<unsigned> v[N];
vector<unsigned long> c[N];
queue<unsigned> q;
void bfs()
{
    int cur=q.front();
    q.pop();
    //viz[cur]=true;
    for(size_t i=0;i<v[cur].size();i++)
    {
        int a=v[cur][i];
        int cst=c[cur][i];
        if(viz[a]) continue;
        q.push(a);
        viz[a]=true;
        if(a>cur)
            cost[a]=cost[cur]+cst;
        else
            cost[a]=cost[cur]-cst;
    }
}
void init()
{
    for(size_t i=0;i<v[1].size();i++)
        cost[v[1][i]]=c[1][i];
}
inline int mod(int x)
{
    if(x>0) return x;
    return -x;
}
int main()
{
    in>>n>>m>>x>>y;
    for(unsigned i=1;i<=m;i++)
    {
        int a,b,d;
        in>>a>>b>>d;
        v[a].push_back(b);
        c[a].push_back(d);
        v[b].push_back(a);
        c[b].push_back(d);
    }
    //init();
    q.push(x);
    viz[1]=true;
    bfs();
    while((!q.empty())&&(!viz[y]))
        bfs();
    out<<mod(cost[x]-cost[y])<<"\n";
    return 0;
}