#include <iostream>
#include<string>
using namespace std;
int find_lucky_ticket(string ticket) {
	char sum1 = 0;
	char sum2 = 0;
	int sum3 = 0;
	for (int i = 0; i < ticket.length() / 2; i++) {
		sum1 += ticket[i];
	}
	for (int j = ticket.length() / 2; j <= ticket.length(); j++) {
		sum2 += ticket[j];
	}
	for (int i = 0; i < ticket.length(); i++) {
		sum3 += ticket[i] -'0';
	}
	if (sum1 == sum2) return sum3;
	return 0;
}
int main() {
	string ticket;
	cout << "Nhap so ve: ";
	cin >> ticket;
	cout << find_lucky_ticket(ticket);
}