// This program was written by Mircea Rebengiuc
// on 03.08.2022
// for problem cbinteractiv

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

int query( int x ){
  int ret;

  printf( "? %d\n", x );
  fflush( stdout );
  scanf( "%d", &ret );

  if( ret == -1 )
    exit( 0 );

  return ret;
}

int main(){
  int st = 0, dr, mij;

  scanf( "%d", &dr );
  while( dr - st > 1 ){
    if( query( mij = (st + dr) >> 1 ) )
      dr = mij;
    else
      st = mij;
  }


  printf( "! %d\n", dr );
  fflush( stdout );
  return 0;
}