import sys
sys.set_int_max_str_digits(0)

from itertools import groupby
def runLengthEncode(S): # list でも str でも OK
    grouped = groupby(S)
    res = []
    for k, v in grouped:
        res.append((k, int(len(list(v)))))
    return res

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

if len(runLengthEncode(S)) == N: # 01010 or 101010
    print('NO')
else:
    print('YES')