# include <bits/stdc++.h>
# define ll long long
# define ld double
# define fi first
# define se second
# define pii pair<int, int>
# define pll pair<ll, ll>
using namespace std;

int main() {
	int N, K;
	scanf("%d %d", &N, &K);
	
	vector<int> arr(N + 1);
	for(int i=1;i<=N;i++) scanf("%d", &arr[i]);
	
	for(int i=K;i<=N;i+=K) {
		for(int c=1;c+i-1<=N;c++) {
			bool ans = 1;
			for(int d=c;d<c+i;d++) {
				if(arr[d] != arr[c + (d - c)%(i / K)]) {
					ans = 0;
					break;
				}
			}
			if(ans) {
				printf("%d\n", i / K);
				for(int d=c;d<c + i /K;d++) printf("%d ", arr[d]);
				printf("\n");
				return 0;
			}
		}
	}
	
	printf("-1\n");
	return 0;
}