from math import sqrt
def Question(x):
    print(f'? {x}')
    return int(input())

def Answer(x):
    print(f'! {x}')
    exit()

def Operator1(x):
    S = []
    for i in range(2,int(sqrt(x))+1):
        while x % i == 0:
            S.append(i)
            x //= i
    if x >= 2:
        S.append(x)
    for bit in range(1<<len(S)):
        x = bit
        z = 1
        for i in S:
            if x & 1:
                z *= i
            x >>= 1
        P[z] = 0

def Operator2(x):
    M = x
    S = []
    for i in range(2,int(sqrt(x))+1):
        while x % i == 0:
            S.append(i)
            x //= i
    if x >= 2:
        S.append(x)
    T = []
    for bit in range(1<<len(S)):
        x = bit
        z = 1
        for i in S:
            if x & 1:
                z *= i
            x >>= 1
        T.append(z)
    for i in range(1,M+1):
        if not i in T:
            P[i] = 0

N = int(input())
P = [1] * (N+1)
for i in range(N,0,-1):
    if P[i]:
        if Question(i) == 1:
            Operator1(i)
        else:
            Operator2(i)
for i in range(N,0,-1):
    if P[i]:
        if Question(i) == i:
            Answer(i)
Answer(1)