#include <iostream>
#include <fstream>
#include <queue>
#include <stack>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
stack < int > s ;
vector < pair < int , int > > G[10001];
int n,m,x,y,vis[10001],p,nr,X,Y; //ar putea sa fie si long llong
void dfs1(int k)
{ vis1[k]=1;
for(int i : G1[k])
{
    if(!vis1[i])
        dfs1(i);
}
s.push(k);
}
void bfs(int st)
{int p1 , p2,nounod;
    s.push_back(st);
    while(!s.empty())
    {
        nounod=s.top();
        for(auto i : G[nounod])
        {
            p1=i.first();
            p2=i.second();
            if (!d[p1])
            {
                d[p1]+=d[nounod]+dist;
                cout<<i.first<<' '<<dist<<'\n';
                q.push(nextnod);
            }
        }
    }
}
int main()
{f>>n>>m>>X>>Y;
for(int i=1;i<=m;++i)
{
    f>>x>>y>>d;
    G[x].push_back({y,d}));
    G[y].push_back({x,-d});
}
bfs(s1);
g<<d[s2]-1;
    return 0;
}