def ask(i,j):
    print("?",i,j,flush=True)
    return int(input())

n=int(input())

for i in range(0,n-1,2):
    j=ask(i,i+1)
    if i==j or i+1==j:
        print("!",j^1,flush=True)
        exit()

print("!",n-1,flush=True)