#010
N=int(input())
S=input()
N2=N//2
nd=0
i=0
while i<=N2 and nd==0:
    j=0
    while j+i+i<N and nd==0:
        if S[j:j+i]==S[j+i+1:j+i+i+1]:
            a="YES"
            nd=1
        j+=1
    i+=1
if i>=N2:
    a="NO"
print(a)