N = int(input())
S = input()
flag = 0

for i in range(len(S)):
    for j in range(i, len(S)):
        try:
            a = S[i - 1:j]
            b = S[j : j + (j + 1 - i)]
        except:
            break
        if a == b:
            print("YES")
            flag = 1
            break
    if flag == 1:
        break

if flag != 1:
    print("NO")