#coding: utf-8

def main():
  n = int(input())
  s = list(map(str, input()))
  print(judge(n, s))


def judge(n, s):
  if n >= 4:
    return 'YES'
  elif n == 1:
    return 'NO'
  else:
    jud = 0
    for i in range(1,n):
      if s[i-1] == s[i]:
        jud +=1
    return 'YES' if jud >= 1 else 'NO'
      

if __name__ == '__main__':
  main()