#include <iostream.h>
#include <fstream.h>
fstream f("cautbin.in",ios::in);
fstream g("cautbin.out",ios::out);
long a[100001],i,N,j;
unsigned m;
int ok;
int main()
{
 f>>N;
 ok=1;
 i=1;
 j=N;
 while ((i<=j) && (ok==0))
			  {
			  m=(i+j)/2;
			  if (a[m]=x) ok=1;
				else {
				      if (a[m]>x) j=m-1;
					      else i=i+1;
				     };
			   };
 if (ok==1) g<<m<<"\n";
      else g<<"-1\n";
 f.close();
 g.close();
 return 0;
}