N = int(input())
import sys

if N % 2 == 1:
    s = set()
    count = 0

    for i in range(0,N - 2,2):
        print("?",i,i + 1)
        a = int(input())
        if a == i:
            print("!",i + 1)
            exit()
        if a == i + 1:
            print("!",i)
            exit()
            
    print("!",N - 1)
            
else:
    for i in range(0,N,2):
        print("?",i,i + 1)
        a = int(input())
        if a == i:
            print("!",i + 1)
        if a == i + 1:
            print("!",i)