#include <algorithm>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
using namespace std;

typedef vector<int> VI;

int main(void) {
    for (int casei = 1; ; ++casei) {
	int n, k; cin >> n >> k;
	if (n == 0) break;

	VI lens;
	for (int i = 0; i < n; ++i) {
	    string s; cin >> s; lens.push_back(s.size());
	}
	sort(lens.begin(), lens.end());

	bool result = true;

	for (int i = 0; i < n; i += k) {
	    double avg = 0.0;
	    for (int j = i; j < i + k; ++j) {
		avg += lens[j];
	    }
	    avg /= k;
	    for (int j = i; j < i + k; ++j) {
		if (abs(lens[j] - avg) > 2.0+1e-6) {
		    result = false;
		}
	    }
	}

	if (casei != 1) printf("\n");
	printf("Case %d: ", casei);
	if (result) printf("yes\n");
	else printf("no\n");
    }
    return 0;
}