#include<complex>
#include<cstdio>
using namespace std;
const int INF=0x3f3f3f3f;
const int N=401,M=6007;
struct node{int v,f,nxt;
}e[M<<1];
int n,m,Enum=1,s,t,ans;
int front[N],cur[N],deep[N],path[N];
int q[N];
bool vis[N];
int qread()
{int x=0;char ch=getchar();while(ch<'0' || ch>'9')ch=getchar();while(ch>='0' && ch<='9'){x=x*10+ch-'0';ch=getchar();}return x;
}
void Insert(int u,int v)
{e[++Enum].v=v;e[Enum].f=1;e[Enum].nxt=front[u];front[u]=Enum;e[++Enum].v=u;e[Enum].nxt=front[v];front[v]=Enum;
}
bool bfs()
{for(int i=0;i<=t;i++){deep[i]=0;cur[i]=front[i];}int head=1,tail=0,u,v;deep[s]=1;q[++tail]=s;while(head<=tail){u=q[head++];for(int i=front[u];i;i=e[i].nxt){v=e[i].v;if(!deep[v] && e[i].f){deep[v]=deep[u]+1;if(v==t)return 1;q[++tail]=v;}}}return 0;
}
int dfs(int x,int cur_flow)
{if(x==t)return cur_flow;int rest=cur_flow,v;for(int &i=cur[x];i;i=e[i].nxt){v=e[i].v;if(deep[v]==deep[x]+1 && e[i].f && rest){int new_flow=dfs(v,min(e[i].f,rest));e[i].f-=new_flow;e[i^1].f+=new_flow;rest-=new_flow;if(new_flow)path[x]=v-n;if(!rest)return cur_flow;}}deep[x]=0;return cur_flow-rest;
}
void Dinic()
{while(bfs())ans+=dfs(s,INF);
}
void print(int x)
{if(!x)return;printf("%d ",x);vis[x]=1;print(path[x]);
}
int main()
{scanf("%d%d",&n,&m);s=0;t=n+n+1;int u,v;for(int i=1;i<=m;i++){u=qread();v=qread();Insert(u,v+n);}for(int i=1;i<=n;i++){Insert(s,i);Insert(i+n,t);}Dinic();for(int i=1;i<=n;i++)if(!vis[i]){print(i);puts("");}printf("%d\n",n-ans);return 0;
}