#include <iostream>
#include <vector>
#include <map>
#include <cmath>
#include <bitset>

using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int x, n, p;
    bitset<32> bits;
    cin >> x >> p;
    int ans = -1;
    for(int i = 1; i <= 32; ++i){
        n = x - i * p;
        bits = n;
        if(i >= bits.count() && i <= n){
            ans = i;
            break;
        }
    }
    cout << ans;



}