import sys

n = int(input())
lo, hi = 1, n

while lo < hi:
    mid = (lo + hi) // 2

    print("? " + str(mid))
    sys.stdout.flush()

    answer = int(input())

    if answer == 1:
        hi = mid
    else:
        lo = mid + 1

print("! " + str(lo))
sys.stdout.flush()