#include<stdio.h>
int main()
{
	long long int n, b;
	scanf("%lld %lld", &n, &b);
	if (n % 2 > 0)
		printf("%lld\n", (n - 1) / 2 % b);
	else if (b % 2 > 0)
		printf("%lld\n", (n - 1 + b) / 2);
	else
		printf("NaN\n");
	return 0;
}