//acmp.ru 0539 tort.cpp 6%

#include <stdio.h>

int main(){
	freopen("INPUT.TXT", "r", stdin);
	freopen("OUTPUT.TXT", "w", stdout);

	short N;
	scanf("%hi", &N);
	if (N <= 1){
		printf("0");
	}else if(N % 2 == 0){
		printf("%hi", N / 2);
	}else if(N % 2 != 0){
		printf("%hi", N);
	}else {
		printf("0");
	}
}