input: Write a function to determine if a given string contains the word "Hello". If it contains "Hello" return True, otherwise return False.
  assert check_hello("Hello, world!")==True
  assert check_hello("Hi there!")==False
  assert check_hello("Say hello to the world!")==False
  assert check_hello("Hello")==True
  assert check_hello("")==False
output: def check_hello(s):
      return "Hello" in s