def main(i: str):
  a = [int(x) for x in i.split(' ')]
  a.sort()

  result = (a[1] - a[0] == 1) and (a[2] - a[1] == 1) and (a[3] - a[2] == 1)
  print('Yes' if result else 'No')

if __name__ == '__main__':
  i: str = input()
  main(i)