def question(x,y):
    print("?",x,y,flush=True)
    z=int(input())
    return z

def answer(k):
    print("!",k,flush=True)
    exit()

def solve():
    N=int(input())
    for t in range(N//2):
        x,y=2*t,2*t+1
        z=question(x,y)
        if z==x:
            answer(y)
        elif z==y:
            answer(x)
    else:
        answer(N-1)

#==================================================
solve()