input: Write a python function to sum prime numbers up to a given number.
  assert sum_prime_numbers(10) == 17  # Primes: 2, 3, 5, 7
  assert sum_prime_numbers(5) == 5    # Primes: 2, 3
  assert sum_prime_numbers(0) == 0    # No primes
  assert sum_prime_numbers(20) == 77  # Primes: 2, 3, 5, 7, 11, 13, 17, 19
output: def sum_prime_numbers(n):
      def is_prime(num):
          if num < 2:
              return False
          for i in range(2, int(num**0.5) + 1):
              if num % i == 0:
                  return False
          return True
      
      return sum(num for num in range(2, n) if is_prime(num))