#include <bits/stdc++.h>

using namespace std;

int main(int argc, char **argv) {
	char buf[64];
	fgets(buf, sizeof(buf), stdin);

	int L, K;
	sscanf(buf, "%d %d", &L, &K);

	int yu = 0;
	for (;;) {
		if ((L -= 2 * K) <= 0) {
			break;
		}
		yu++;
	}

	printf("%d\n", K * yu);
	return 0;
}