#include <iostream>;
#include <vector>;
using namespace std;
int main() {
	ios_base::sync_with_stdio(0);
	freopen ("tickets.in", "r", stdin);
	freopen ("tickets.out", "w", stdout);

	int n,m, t, count=0;

	cin>>n>>m;

	int a[n];

	for(int i = 1; i <=n; i++) a[i] = 0;

	for(int i = 1; i <= m; i++){
		cin>>t;
		a[t]++;
	}

	for(int i = 1; i <=n; i++){

		if(a[i] > 1) count++;

	}
	cout<<count<<"\n";

	if(count == 0) return 0;

	for(int i = 1; i <= n; i++){

		if(a[i] > 1) cout<<i<<" ";

	}
	return 0;
}