BBBB

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

using namespace std;

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

vector<int> par[N];
vector<vector<int>> ans;
vector<bool> 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].push_back(b);
  }
  vector<int> vec;
  for (int i = 1; i <= n; i++)
  {
    vec.push_back(i);
  }
  do
  {
    flag = true;
    used = vector<bool>(n, false);
   for (auto v : vec)
   {
     for (auto pr: par[v])
     {
       if (!used[pr])
       {
         flag = false;
         break;
       }
     }
     if(!flag)
        break;
     used[v] = true;
   }
   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 << " ";
      }
      cout << endl;
    }
  }
  else cout << "no";
	return 0;
}