#include <library.h>

int count_ones(int N, int mask = 1)
{ if (mask == 0)
    return 0;
  if ((N & mask) == 0)
    return count_ones(N, mask << 1);
  else
    return 1 + count_ones(N, mask << 1); }

int main()
{ cout << "Enter a number: ";
  const int x = read_int();
  cout << count_ones(x) << "\n"; }