#include <bits/stdc++.h>
using namespace std;
#define repf(i,k,n) for(int i=k; i<n; i++)
#define rep(i,n) for(int i=0; i<n; i++)
#define all(v) v.begin(), v.end()
#define SZ(v) int(v.size())
typedef vector<int> vi;

//QOJ.ac 2nd Uni Cap - stage 16 F
int main(){ 
	ios::sync_with_stdio(0); cin.tie(0);
	int n,m; cin>>n>>m;
	vector<vi> adj(n);
	rep(i,m){
		int a,b; cin>>a>>b;
		a--;b--;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	int mx1=0,mx2=0;
	rep(i,n){
		mx2=max(mx2,SZ(adj[i]));
		if(mx2>mx1) swap(mx2,mx1);
	}
	if(mx1-mx2>=5){
		cout << "ok" << '\n';
		return 0;
	}
	rep(i,n) if(SZ(adj[i])==mx1){
		cout << 5 << '\n';
		sort(all(adj[i]));
		int j=0,k=0;
		rep(t,5){
			while(adj[i][k]<j) k++;
			while(adj[i][k]==j) j++,k++;
			cout << i+1 << ' ' << j+1 << '\n';
			j++;
		}
	}
	
	return 0;
}