#define _CRT_SECURE_NO_WARNINGS 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
	char a1[] = { 0 };
	char a2[] = { 0 };
	int i, a = 0;
	float c;
	scanf("%f", &c);
	scanf("%c", &a1);
	scanf("%c", &a2);
	int len = strlen(a1);
	for (i = 0; i < len; i++)
	{
		if (a1[i] == a2[i]) a++;
	}
	float b = len * c;
	if (a > b) printf("yes");
	else printf("no");
	return 0;
}