import strutils
let
  N = stdin.readline.parseInt
  S = stdin.readline

proc main =
  for i in 0..<N-1:
    if S[i] == S[i+1]:
      echo("YES")
      return
  for i in 0..<N-3:
    if S[i] != S[i+1] and S[i+1] != S[i+2] and S[i+2] != S[i+3]:
      echo("YES")
      return
  echo("NO")
main()