#include<bits/stdc++.h>
using namespace std;

vector<vector<int> > g;
vector<vector<int> > rg;
vector<int> dependencies;
vector<vector<int> > graph;
int n;
void getDependence(int f, int & ans) {
  ans |= (1<<f);
  for(int v : rg[f]) {
    if((ans & (1<<v)) == 0)
      getDependence(v, ans);
    ans |= (1<<v);
  }
}

int checkBit(int val, int bit) {
  return (val>>bit)&1;
}
vector<vector<int> > answer;

int getNextBit(int mask, int nxt) {
  int answer = 0;
  nxt -= mask;
  while(nxt) {
    answer++;
    nxt /= 2;
  }
  return answer;
}

void buildAnswer(int mask, vector<int> v) {
  if(mask == (1<<n) - 1) {
    answer.push_back(v);
    return;
  }
  for(int nextMask : graph[mask]) {
    vector<int> nextVector = v;
    nextVector.push_back(getNextBit(mask, nextMask));
    buildAnswer(nextMask, nextVector);
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin>>n;
  g.resize(n);
  rg.resize(n);
  dependencies.resize(n, 0);
  int m;
  cin>>m;
  for(int i=0; i<m; i++) {
    int f,t;
    cin>>f>>t;
    g[f - 1].push_back(t - 1);
    rg[t - 1].push_back(f - 1);
  }
  for(int i=0; i<n; i++) {
    getDependence(i, dependencies[i]);
  }

  set<int> values;
  for(int val : dependencies) {
    if(values.find(val) != values.end()) {
      cout<<"no";
      return 0;
    }
    values.insert(val);
  }


  graph.resize(1<<n);

  for(int mask = 0; mask < (1<<n); mask++) {
    for(int bit = 0; bit < n; bit++) {
      if(!checkBit(mask, bit)) {
        int nextMask = (mask + (1<<bit));
        if((dependencies[bit] & nextMask) == dependencies[bit]) {
          graph[mask].push_back(nextMask);
        }
      }
    }
  }

  buildAnswer(0, {});

  cout<<answer.size()<<endl;
  for(vector<int> & v : answer) {
    for(int val : v) {
      cout<<val<<" ";
    }
    cout<<"\n";
  }

  return 0;
}