#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;
 
int visited[1000001];
 
void DFS(unordered_map<int,unordered_map<int,int> >& Map,int*visited,int i)
{
	//cout<<"i="<<i<<endl;
	visited[i]=1;
 
	for(auto it=Map[i].begin();it!=Map[i].end();it++)
	{
		if(visited[it->first] == 0)
		{
			DFS(Map,visited,it->first);
		}
	}
}
 
 
int main() {
 
	int n,m;
	cin>>n>>m;
 
	unordered_map<int,unordered_map<int,int> > Map;
	for(int i=0;i<m;i++)
	{
		int x,y;
		cin>>x>>y;
		Map[x-1][y-1]=1;
		Map[y-1][x-1]=1;
	}
 
	for(int i=0;i<n;i++)
	{
		visited[i]=0;
	}
 
	int count1=0;
	vector<int> bridges;
	for(int i=0;i<n;i++)
	{
		if(visited[i] == 0)
		{
			bridges.push_back(i+1);
			DFS(Map,visited,i);
			count1++;
		}
	}
 
	cout<<bridges.size()-1<<endl;
	for(int i=0;i<bridges.size()-1;i++)
	{
		cout<<bridges[i]<<" "<<bridges[i+1]<<endl;
	}
 
 
	return 0;
}

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