//minamoto

 #include<iostream>

 #include<cstdio>

 #include<queue>

 #include<cstring>

 using namespace std;

 #define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)

 char buf[<<],*p1=buf,*p2=buf;

 inline int read(){

     #define num ch-'0'

     char ch;bool flag=;int res;

     while(!isdigit(ch=getc()))

     (ch=='-')&&(flag=true);

     for(res=num;isdigit(ch=getc());res=res*+num);

     (flag)&&(res=-res);

     #undef num

     return res;

 }

 char sr[<<],z[];int C=-,Z;

 inline void Ot(){fwrite(sr,,C+,stdout),C=-;}

 inline void print(int x){

     if(C><<)Ot();

     while(z[++Z]=x%+,x/=);

     while(sr[++C]=z[Z],--Z);

 }

 const int N=,M=,inf=0x3f3f3f3f;

 int head[N],Next[M],ver[M],edge[M],cur[N],las[N],tot=,vis[N];

 int n,m,s,t,dep[N];

 queue<int> q;

 inline void add(int u,int v,int e){

     ver[++tot]=v,Next[tot]=head[u],head[u]=tot,edge[tot]=e;

     ver[++tot]=u,Next[tot]=head[v],head[v]=tot,edge[tot]=;

 }

 bool bfs(){

     while(!q.empty()) q.pop();

     memset(dep,-,sizeof(dep));

     for(int i=;i<=*n+;++i) cur[i]=head[i];

     q.push(s),dep[s]=;

     while(!q.empty()){

         int u=q.front();q.pop();

         for(int i=head[u];i;i=Next[i]){

             int v=ver[i];

             if(dep[v]<&&edge[i]){

                 dep[v]=dep[u]+,q.push(v);

                 if(v==t) return true;

             }

         }

     }

     return false;

 }

 int dfs(int u,int limit){

     if(!limit||u==t) return limit;

     int flow=,f;

     for(int i=cur[u];i;i=Next[i]){

         int v=ver[i];cur[u]=i;

         if(dep[v]==dep[u]+&&(f=dfs(v,min(limit,edge[i])))){

             flow+=f,limit-=f;

             edge[i]-=f,edge[i^]+=f;

             las[u]=v;

             if(!limit) break;

         }

     }

     return flow;

 }

 int dinic(){

     int flow=;

     while(bfs()) flow+=dfs(s,inf);

     for(int i=;i<=n;++i)

     if(!vis[i]){

         int now=i;

         print(now),sr[++C]=' ';

         vis[now]=;

         while(las[now]){

             print(las[now]-n),sr[++C]=' ';

             now=las[now]-n;

             vis[now]=;

         }

         sr[++C]='\n';

     }

     return flow;

 }

 int main(){

     n=read(),m=read();

     s=,t=*n+;

     for(int i=;i<=n;++i) add(s,i,),add(i+n,t,);

     for(int i=;i<=m;++i){

         int u=read(),v=read();

         add(u,v+n,);

     }

     print(n-dinic()),sr[++C]='\n';

     Ot();

     return ;

 }