#include<bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
    ll V,E,S,G;
    cin>>V>>E>>S>>G;
    set<array<ll,2>> EDGE_set;
    for(int i=0;i<E;i++){
        ll A,B;
        cin>>A>>B;
        if(A>B)swap(A,B);
        assert(!EDGE_set.count({A,B}));
        EDGE_set.insert({A,B});
    }
}