BBBBBB

#include <bits/stdc++.h>
#include <algorithm>

using namespace std;

using ll = long long;
constexpr int N = 13;

int par[N];
vector<vector<int>> ans;
vector<int> vec;
int used;
bool flag = true;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int n, m, b, p;
  cin >> n >> m;
  while(m--)
  {
    cin >> b >> p;
    par[p-1]+=(1<<(b-1));
  }
  for (int i = 0; i < n; i++)
    vec.push_back(i);
  do
  {
    flag = true;
    used = 0;
    for (auto el : vec)
    {
      if ((par[el] & used)!=par[el])
      {
        flag = false;
        break;
      }
      used+=1<<el;
    }
    if (flag)
    {
      ans.push_back(vec);
    }
  } while (next_permutation(vec.begin(), vec.end()));
	if (ans.size())
  {
    cout << ans.size() << endl;
    for (auto a : ans)
    {
      for (auto el : a)
      {
        cout << el+1 << " ";
      }
      cout << endl;
    }
  }
  else cout << "no";
	return 0;
}