#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
	int lk[2];
	char str[32], *ch;
	fgets(str, sizeof(str), stdin);
	ch = strtok(str, " \n");
	for (int i = 0; i < 2; i++) {
		if (ch == NULL) break;
		else lk[i] = atoi(ch);
		ch = strtok(NULL, " \n");
	}
	int i = 0;
	int sum = 0;
	while (lk[0] > sum) {
		sum += lk[1] << 1;
		if (lk[0] > sum) i++;
	}
	printf("%d\n", lk[1] * i);
	return 0;
}