#include<iostream>
#include<cstring>
#define max(a,b) (a>b?a:b)
#define N 1000
using namespace std;
int s=0,n;
char a[N],b[N];
double ss;
int main()
{
	scanf("%lf%s%s",&ss,a,b);
	n=max(strlen(a),strlen(b));
	for(int i=0;i<n;i++) if(a[i]==b[i]) s++;
	printf("%s\n",(n*1.0/s>=ss?"yes":"no"));
	return 0;
}