#include <bits/stdc++.h>
#define rep(i,j,n) for(register int i=j;i<=n;i++)
#define Rep(i,j,n) for(register int i=j;i>=n;i--)
#define low(x) x&(-x)
using namespace std ;
typedef long long LL ;
const int inf = INT_MAX >> 1 ;
inline LL In() { LL res(0) , f(1) ; register char c ;
#define gc c = getchar()
while(isspace(gc)) ; c == '-' ? f = - 1 , gc : 0 ;
while(res = (res << 1) + (res << 3) + (c & 15) , isdigit(gc)) ;
return res * f ;
#undef gc
}
double x ;
string s1 , s2 ;
inline void Ot() {
cin >> x ;
getchar() ;
getline(cin , s1) ;
getline(cin , s2) ;
int len = s1.length() ;
int ans(0) ;
rep(i,1,len) if(s1[i-1] == s2[i-1]) ans ++ ;
double y = ans*1.0 / len ;
puts(x < y ? "yes" : "no") ;
}
signed main() {
// freopen("test.in","r",stdin) ;
return Ot() , 0 ;
}