#include<iostream>

using namespace std;

int main(){

  int k,n,z=0,f;
  cin >> k >> n;
  int flag = 1;
  f = n;
  while(flag == 1){

    if(n<k/2){
      z += f;
      flag = 1;
      n += f;
    }else
      flag = 0;
  }

  cout << z << endl;

  return 0;
}