#include <bits/stdc++.h>

void solve() {
    int n;
    std::cin >> n;
    auto dfs = [&](auto self, int l, int r, int v) -> void {
        if(l == r) {
            std::cout << "! " << l << std::endl;
            exit(0);
        }
        int mid = (l + r) >> 1;
        std::cout << "? " << l << std::endl;
        int val;
        std::cin >> val;
        if(val == v) {
            std::cout << "! " << l << std::endl;
            exit(0);
        }
        std::cout << "? " << mid << std::endl;
        int val2;
        std::cin >> val2;
        if(val == val2) {
            std::cout << "! " << mid << std::endl;
            exit(0);
        }
        if(val + 1 == val2) {
            self(self, mid + 1, r, val2);
        } else {
            self(self, l + 1, mid - 1, val2);
        }
    } ;
    dfs(dfs, 1, n, 0);
}

int main() {
    std::cin.tie(nullptr) -> sync_with_stdio(false);
    int T = 1;
    while(T--) solve();
    return 0;
}