#include<stdio.h>
#include<algorithm>
using namespace std;
 
int n,k,rest,cat,sol;
 
int main ()
{
        freopen("subset2.in","r",stdin);
        freopen("subset2.out","w",stdout);
 
        scanf("%d%d",&n,&k);
 
        cat = n / k;
        rest = n % k;
        if(k & 1)
        {
                rest = min(rest, k / 2);
                sol = rest * (cat + 1) + (k / 2 - rest) * cat + 1;
        }
        else
        {
                rest = min(rest, k / 2 - 1);
                sol = rest * (cat + 1) + (k / 2 - 1 - rest) * cat + 2;
        }
        printf("%d\n",sol);
 
        return 0;
}