#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

const char iname[] = "felinare.in";
const char oname[] = "felinare.out";

ifstream fin(iname);
ofstream fout(oname);

int n, m, i, x, y, cuplat, c, viz[8900], R[8900], L[8900];
vector<int> Gr[8900];

int pair_up(int nod)
{	
	if(viz[nod] == 1)
		return 0;
	viz[nod] = 1;
	for(vector<int>::iterator it = Gr[nod].begin(); it != Gr[nod].begin(); ++it)
		if(pair_up(R[*it]))
		{
			L[nod] = *it;
			R[*it] = nod;
			return 1;
		}
}
		
		
int main()
{
	fin >> n >> m;
	for(i = 1; i <= m; i ++)
	{
		fin >> x >> y;
		Gr[x].push_back(y);
	}
	
	cuplat = 1;
	while(cuplat)
	{	
		for(i = 1; i <= n; i ++)
			viz[i] = 0;
		cuplat = 0;
		for(i = 1; i <= n; i ++)
			if(L[i] == 0)
				if(pair_up(i))
					++c, cuplat = 1;
	}
				
	fout << c << "\n";
	for(i = 1; i <= n; i ++)
		if(L[i])
			fout << i << " " << L[i] << "\n";
	return 0;
}