#include <iostream>

using namespace std;

int put[5000001];
int k,d;
int i;
int x,nr;


int main()
{
	freopen("pascal.in","r",stdin);
	freopen("pascal.out","w",stdout);

	scanf("%d %d\n", &k, &d);

	for ( i = 1; i <= k; i ++ )
	{
		put[i] = put[i-1];
		if ( i%d == 0 )
			put[i] += i/d;
	}

	for ( i = 1; i <= k; i++ )
	{
		x = put[k] - ( put[k-i] + put[i] );
		if ( x > 0 ) nr++;
	}

	printf("%d\n", nr );

	fclose(stdout);
	fclose(stdin);

	return 0;
}