#include <bits/stdc++.h>
using namespace std;

double k;
int cnt=0;
string s1,s2;
int main(){
	cin>>k;
	cin>>s1>>s2;
	for(int i=0;i<s1.size();i++){
		if(s1[i]==s2[i]) cnt++;
	}
	if(cnt*1.0/s1.size()>k) cout<<"yes";
	else cout<<"no";
	return 0;
}