#include <bits/stdc++.h>
int main(void) {
  int n = 0;
  int d = 0;
  int a;
  int b;
  scanf("%d%d", &n, &d);
  for (a = 0; (2 * d + 1) * a < n; a++) {
    b = a;
  }
  printf("%d", b + 1);
  return 0;
}
