import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################


n = ni()
for i in range(n//2):
    x = i * 2
    y = (i*2+1)%n
    print("?", x, y, flush=True)
    z = ni()
    if z == x:
        print("!", y, flush=True)
        exit()
    if z == y:
        print("!", x, flush = True)
        exit()
print("!", n-1, flush=True)