//
//  main.cpp
//  wang24.3
//
//  Created by Candy on 29/11/2016.
//  Copyright © 2016 Candy. All rights reserved.
//

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int N=2005,M=1e6,INF=1e9;
int read(){char c=getchar();int x=0,f=1;while(c<'0'||c>'9'){if(c=='-')f=-1; c=getchar();}while(c>='0'&&c<='9'){x=x*10+c-'0'; c=getchar();}return x*f;
}
int n,m,s,t,u,v;
struct edge{int v,ne,c,f;
}e[M<<1];
int cnt,h[N];
inline void ins(int u,int v,int c){cnt++;e[cnt].v=v;e[cnt].c=c;e[cnt].f=0;e[cnt].ne=h[u];h[u]=cnt;cnt++;e[cnt].v=u;e[cnt].c=0;e[cnt].f=0;e[cnt].ne=h[v];h[v]=cnt;
}
int vis[N],d[N],q[N],head=1,tail=1;
bool bfs(){memset(vis,0,sizeof(vis));memset(d,0,sizeof(d));head=tail=1;q[tail++]=s;d[s]=0;vis[s]=1;while(head!=tail){int u=q[head++];for(int i=h[u];i;i=e[i].ne){int v=e[i].v;if(!vis[v]&&e[i].c>e[i].f){vis[v]=1;d[v]=d[u]+1;q[tail++]=v;if(v==t) return true;}}}return false;
}
int cur[N];
int dfs(int u,int a){if(u==t||a==0) return a;int flow=0,f;for(int &i=cur[u];i;i=e[i].ne){int v=e[i].v;if(d[v]==d[u]+1&&(f=dfs(v,min(a,e[i].c-e[i].f)))>0){flow+=f;e[i].f+=f;e[((i-1)^1)+1].f-=f;a-=f;if(a==0) break;}}return flow;
}
int dinic(){int flow=0;while(bfs()){for(int i=s;i<=t;i++) cur[i]=h[i];flow+=dfs(s,INF);}return flow;
}
int to[N],ind[N];
void print(){for(int u=1;u<=n;u++)for(int i=h[u];i;i=e[i].ne){int v=e[i].v;if(e[i].c==1&&e[i].f==1) to[u]=v-n,ind[v-n]++;}for(int i=1;i<=n;i++) if(!ind[i]){int u=i;while(u!=0) printf("%d ",u),u=to[u];putchar('\n');}
}
int main(int argc, const char * argv[]) {n=read();m=read();s=0;t=n+n+1;for(int i=1;i<=m;i++){u=read();v=read();ins(u,n+v,1);}for(int i=1;i<=n;i++) ins(s,i,1),ins(n+i,t,1);int ans=n-dinic();print();printf("%d",ans);return 0;
}