#include <cstdio>
#include <vector>
#define dim 260

using namespace std;

int n, m, fol[dim], l[dim], r[dim];
vector<int> g[dim], a[dim];

int pairup(int x)
{
	vector<int>::iterator it;
	if (fol[x]) return 0;
	fol[x]=1;
	for (it=g[x].begin(); it!=g[x].end(); it++)
		if (!r[*it])
		{
			l[x]=*it;
			r[*it]=x;
			return 1;
		}
	for (it=g[x].begin(); it!=g[x].end(); it++)
		if (pairup(r[*it]))
		{
			l[x]=*it;
			r[*it]=x;
			return 1;
		}
	return 0;
}

int main()
{
	int i, x, y, count=1;
	freopen("strazi.in", "r", stdin);
	freopen("strazi.out", "w", stdout);
	scanf("%d %d\n", &n, &m);
	for (i=1; i<=m; i++)
	{
		scanf("%d %d\n", &x, &y);
		g[x].push_back(y);
	}
	
	while (count)
	{
		count=0;
		memset(fol, 0, sizeof(fol));
		for (i=1; i<=n; i++)
			if (!l[i]) count|=pairup(i);
	}
	
	count=-1;
	for (i=1; i<=n; i++)
	{
		if (r[i]) continue;
		count++;
		x=i;
		do
		{
			a[count].push_back(x);
			x=l[x];
		} while (x);
	}
	
	printf("%d\n", count);
	for (i=0; i<count; i++)
		printf("%d %d\n", a[i].back(), a[i+1].front());
	for (i=0; i<=count; i++)
		for (vector<int>::iterator it=a[i].begin(); it!=a[i].end(); it++)
			printf("%d ", *it);
	printf("\n");
	return 0;
}