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

int main() {

    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    int n,k;
    scanf("%d %d\n",&n,&k);
    if(n==k*2+1)
    printf("%d",(n/(2*k+1)));
    return 0;
}