#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define int long long
#define ll long long
#define ld long double
#define ar array
#define all(v) v.begin(), v.end()
using namespace std;
const int N = 5e5 + 20;
const int LOG = 20;
const int INF = 1e12;
const int MOD = 1e9 + 7;
void chmin(int &x,int y){x = min(x, y);};
void chmax(int &x,int y){x = max(x, y);};
void mm(int &x){x = (x % MOD + MOD) % MOD;};
vector<int> g[N];
signed main(){ios_base::sync_with_stdio(false);cin.tie(0);
int n, m;
cin>>n>>m;
while(m--){
int a, b;
cin>>a>>b;
--a, --b;
g[a].push_back(b);
g[b].push_back(a);
}
vector<int> ans;
bool b[n] = {0};
for(int i = 0;i < n;i++){
if(!b[i]){
for(auto u: g[i])b[u] = 1;
}
}
for(int i = 0;i < n;i++){
if(!b[i])ans.push_back(i + 1);
}
cout<<ans.size()<<'\n';
for(auto u: ans)cout<<u<<' ';
}
