#include<bits/stdc++.h>
#define ff first
#define ss second
#define pb push_back
typedef long long ll;
using namespace std;
typedef pair<int,int> pii;

const int mod=998244353;
inline int add(int x,int y){int ret=x+y;if(ret>=mod)ret-=mod;return ret;}
inline int sub(int x,int y){int ret=x-y;if(ret<0)ret+=mod;return ret;}
inline int mul(int x,int y){return ((ll)x*y)%mod;}
inline int step(int base,int pw){int ret=1;while(pw){if(pw&1)ret=mul(ret,base);base=mul(base,base);pw>>=1;}return ret;}
inline int invv(int x){return step(x,mod-2);}


const int maxn=2e5+10;

struct edge{
    int u,v,f;
};
vector<edge>e;
vector<int>g[maxn];
int start[maxn],level[maxn],source,sink;

int n,m;


void add_edge(int u,int v){
    g[u].pb(e.size());
    e.pb({u,v,0});
    g[v].pb(e.size());
    e.pb({v,u,1});
}

int bfs(){

    memset(level,0,sizeof(level));
    level[source]=1;
    queue<int>q;
    q.push(source);
    while(q.size()){

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

        for(int i=0;i<g[x].size();i++){
            int id=g[x][i];
            if(e[id].f || level[e[id].v])continue;
            level[e[id].v]=level[x]+1;
            q.push(e[id].v);
        }

    }

    return level[sink];
}
int sflow(int x){

    if(x==sink)return 1;

    for(;start[x]<g[x].size();start[x]++){

        int id=g[x][start[x]];

        if(e[id].f==0 && level[x]+1==level[e[id].v]){

            int tmp=sflow(e[id].v);

            if(tmp){
                e[id].f^=1;
                e[id^1].f^=1;
                return 1;
            }

        }

    }

    return 0;
}
vector<pii>get_match(){

    vector<pii>ret;

    while(bfs()){
        memset(start,0,sizeof(start));
        while(sflow(source)){}
    }

    for(int i=1;i<=n;i++){
        for(int j=0;j<g[i].size();j++){
            int id=g[i][j];
            if(e[id].v==source)continue;
            if(e[id].f)ret.pb({i,e[id].v});
        }
    }

    return ret;
}

vector<int>vect[maxn],vect2[maxn];
bitset<maxn>cmask,cmask2;/// hendlaj
int reach[maxn],reach2[maxn];
int rez[maxn];

void drugi_edge(int u,int v){
    ///vect[u].pb(v);
    vect[v].pb(u);
    vect2[u].pb(v);
    ///printf("%d %d EDGE\n",u,v);
}


int main(){

    ///freopen("test.txt","r",stdin);

    scanf("%d %d",&n,&m);
    vector<pii>myedges;
    for(int i=1;i<=m;i++){
        int u,v;
        scanf("%d %d",&u,&v);
        add_edge(u,v+n);
        myedges.pb({u,v+n});
    }
    source=0;
    sink=2*n+1;
    for(int i=1;i<=n;i++){
        add_edge(source,i);
        add_edge(i+n,sink);
        rez[i]=2;
        cmask[i]=1;
        cmask2[i]=1;
    }

    vector<pii> mat=get_match();


    printf("%d\n",n-1-mat.size());

    if(n-1-mat.size()==0){
        printf("\n");
        return 0;
    }

    set<pii>st;
    queue<int>q;
    for(int i=0;i<mat.size();i++){
        ///printf("%d %d MATCH\n",mat[i].ff,mat[i].ss);

        int u,v;
        u=mat[i].ff;
        v=mat[i].ss;

        drugi_edge(v,u);
        st.insert({u,v});

        cmask[v-n]=0;
        cmask2[u]=0;

        rez[u]--;
        rez[v-n]--;
    }
    ///for(int i=1;i<=n;i++)printf("%d %d AFA\n",i,rez[i]);
    for(int i=1;i<=n;i++)if(cmask[i]){q.push(i+n);reach[i+n]=1;}
    for(int i=0;i<myedges.size();i++){
        int u,v;
        u=myedges[i].ff;
        v=myedges[i].ss;

        if(st.find({u,v})==st.end()){
            drugi_edge(u,v);
        }

    }

    /*for(int i=1;i<=n;i++){
        printf("%d %d REZ\n",i,rez[i]);
    }*/

    while(q.size()){
        int x=q.front();
        q.pop();

        for(int i=0;i<vect[x].size();i++){
            int id=vect[x][i];
            if(reach[id])continue;
            reach[id]=1;
            q.push(id);
        }
    }

    for(int i=1;i<=n;i++){
        if(cmask2[i]){
            q.push(i);
            reach2[i]=1;
            ///printf("strt %d\n",i);
        }
    }
    while(q.size()){
        int x=q.front();
        q.pop();
        ///printf("%d DOSO\n",x);

        for(int i=0;i<vect2[x].size();i++){
            int id=vect2[x][i];
            if(reach2[id])continue;
            reach2[id]=1;
            q.push(id);
        }
    }

    //for(int i=1;i<=n;i++)printf("%d %d AFA\n",i,rez[i]);
    for(int i=0;i<mat.size();i++){

        int u,v;
        u=mat[i].ff;
        v=mat[i].ss;
        int pom=reach[u];
        rez[v-n]+=pom;

        pom=reach2[v];
        rez[u]+=pom;

        ///printf("%d %d | %d %d PROBAJ\n",u,v,reach[u],reach2[v]);

    }
    //printf("%d %d AA\n",reach2[15],reach[1]);

   // for(int i=1;i<=n;i++)printf("%d %d AFA\n",i,rez[i]);

    for(int i=1;i<=n;i++){
        if(rez[i]>0)printf("%d ",i);
    }
    printf("\n");


    return 0;
}