N=int(input())

for i in range(0,N-1,2):
    print("?",i,i+1, flush=True)
    z=int(input())
    if z==i:
        print("!",i+1,flush=True)
        break
    elif z==i+1:
        print("!",i,flush=True)
        break
else:
    print("!",N-1,flush=True)