#include <iostream>
using namespace std;
 
int main() {
	const int TWO = 2;
	const int TEN = 10;
	int number, digits_sum = 0;
	cin >> number;
	while (number > 0) {
		digits_sum += number % TEN;
		number /= TEN;
	}
	int is_prime = 1;
	for (int divisor = TWO; divisor < digits_sum; ++divisor) {
		if (digits_sum % divisor == 0) {
			is_prime = 0;
		}
	}
	if (is_prime == 1 && digits_sum != 1) {
		digits_sum *= TWO;
	} else {
		digits_sum /= TWO;
	}
	cout << digits_sum;
	return 0;
}

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

CjEyMzQ3IC0mZ3Q7IDM0Cg==

12347 -> 34