import sys
input = sys.stdin.readline
n=int(input())
if n%2==0:
  for i in range(n//2-1):
    print("?",i*2,i*2+1,flush=True)
    z=int(input())
    if z==i*2:
      print("!",i*2+1,flush=True)
      exit()
    elif z==i*2+1:
      print("!",i*2,flush=True)
      exit()
  x=(n//2-2)*2+2
  print("?",x,x-1,flush=True)
  z=int(input())
  if z==x-1:
    print("!",x,flush=True)
  else:
    print("!",x+1,flush=True)
else:
  for i in range(n//2):
    print("?",i*2,i*2+1,flush=True)
    z=int(input())
    if z==i*2:
      print("!",i*2+1,flush=True)
      exit()
    elif z==i*2+1:
      print("!",i*2,flush=True)
      exit()
  x=(n//2-1)*2+2
  print("!",x,flush=True)