поиск количества единиц

#include <iostream>
using namespace std;

void edinica( long long l, long long n, long long m)
{
  int middle = 0;

  if (n-l==1)
  {
   cout << "! " << m-n << endl;
  }
  else
  {
    long long i=(n-l)/2+1+l;

     cout << "?" << " " << i << endl;
     cin >> middle;

     if (middle == 1)
      {
       n=i-1;
       edinica ( l, n, m);
      }
     else//проверяем вторую половину
     {
        l=i-1;
        edinica ( l, n, m);
     }
  }
}

int main()
{
 cout.flush();

 long long n=0;
 int first_element=0, last_element=0;

 cin >> n;

cout << "?" << " " << 1 << endl;
  cin >> first_element;

cout << "?" << " " << n << endl;
  cin >> last_element;

if (first_element == 1)
 cout << "!" << " " << n << endl;
 else if (last_element == 0)
  cout << "!" << " " << 0 << endl;
    else edinica(0, n-1, n);
}