import sys

N = int(input())
for i in range(N//2):
    print("? {0} {1}".format(2 * i, 2 * i + 1), flush=True)
    z = int(input())
    if z == 2 * i:
        print("! {0}".format(2 * i + 1), flush=True)
        exit()
    elif z == 2 * i + 1:
        print("! {0}".format(2 * i), flush=True)
        exit()
print("! {0}".format(N - 1), flush=True)