#include <bits/stdc++.h>

using i64 = long long;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int N;
    std::cin >> N;
    
    for (int i = 0; i + 1 < N; i += 2) {
        std::cout << "? " << i << " " << i + 1 << std::endl;
        int res;
        std::cin >> res;
        if (res == i) {
            std::cout << "! " << i + 1 << std::endl;
            return 0;
        }
        if (res == i + 1) {
            std::cout << "! " << i << std::endl;
            return 0;
        }
    }
    
    std::cout << "! " << N - 1 << std::endl;
    
    return 0;
}