Sums of Prime/Non prime numbers

command = ''
sum_prime_numbers = 0
sum_non_prime_numbers = 0
while command != 'stop':
    command = input()
    if command == 'stop':
        break
    number = int(command)
    if number < 0:
        print(f'Number is negative.')
    else:
        i = 2
        isprime = False
        for i in range(2, number):
            if number % i == 0:
                sum_non_prime_numbers += number
                isprime=True
                break
        if (isprime==False):
            sum_prime_numbers += number
print(f'Sum of all prime numbers is: {sum_prime_numbers}')
print(f'Sum of all non prime numbers is: {sum_non_prime_numbers}')