import sys
from collections import deque, Counter
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353

def query(x, y):
    print('?', x, y, flush=True)
    return ii()

def answer(z):
    print('!', z, flush=True)
    exit()


n = ii()

for i in range(0, n - 1, 2):
    z = query(i, i + 1)
    if z == i:
        answer(i + 1)
    elif z == i + 1:
        answer(i)
answer(n - 1)