# your code goes here
#010
N=int(input())
S=input()
N2=N//2
nd=0
#for i in range(N-2):
 #   if S[i]==s[i+1]:
   #     a="YES"
     #   nd=1
i=1
while i<=N2+1 and nd==0:
    j=0
    #print(S[j:j+i])
    while j+i+i<N+1 and nd==0:
        if S[j:j+i]==S[j+i:j+i+i]:
            a="YES"
            nd=1
        j+=1
    i+=1
if nd==0:
    a="NO"
print(a)