N = int(input())
S = input()

for i in range(1, N):
    for j in range(i, N):
        if j+(j+1-i) > N:
            continue
        if S[i-1: j] == S[j : j+(j+1-i)]:
            print('YES')
            break
    else:
        continue
    break
else:
    print('NO')