#include <bits/stdc++.h>
using namespace std;

// TLEするコード
int main() {
    int N, M;
	scanf("%d",&N,&M);
	int A[N];
    for(int i = 0; i < N; i++)
        scanf("%d",&A[i]);
    sort(A,A+N);
    vector<int> B;
    for(int i = 1; i < N; i++) {
        for(int j = A[i]; j <= M; j += A[i]) {
            if(!binary_search(A, A+N, j)) {
				printf("-1\n");
                return 0;
            }
        }
        bool ret = true;
        for(int j=0;j<(int)(B.size());j++){
        	if(B[j]>(A[i]/2)) break;
        	if(A[i]%B[j]==0){
        		ret=false;
        	}
        }
        if(ret)
            B.emplace_back(A[i]);
    }
	printf("%d\n",(int)(B.size()));
    for(int i = 0; i < (int)B.size(); i++) {
		printf("%d ",B[i]);
    }
	printf("\n");
}