#include <stdio.h>
#include <string.h>

int main(void)
{
	int n, m;
	char s[50][51];
	char cat[2501] = "\0";
	int judge = 0;
	int i;

	scanf("%d %d", &n, &m);

	for (i = 0; i < n; i++) {
		scanf("%s", &s[i]);
		strcat(cat, s[i]);
	}
	
	for (i = 0; i < strlen(cat) - 3; i++) {
		if (cat[i] == 'L' && cat[i + 1] == 'O' && cat[i + 2] == 'V' && cat[i + 3] == 'E') {
			judge = 1;
			break;
		}
	}

	printf("%s\n", judge ? "YES" : "NO");

	return 0;
}