input: Write a function to find the next prime number after a given number.
  assert find_prime_number(10)==11
  assert find_prime_number(14)==17
  assert find_prime_number(20)==23
output: def find_prime_number(n):
      def is_prime(x):
          if x < 2:
              return False
          for i in range(2, int(x**0.5) + 1):
              if x % i == 0:
                  return False
          return True
  
      next_number = n + 1
      while not is_prime(next_number):
          next_number += 1
      return next_number