#include <bits/stdc++.h>
using namespace std;

#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
template <typename ...T>
void debug_(const char *s, T ...a) {
    cerr << "\e[1;32m(" << s << ") = (";
    int cnt = sizeof...(T);
    (..., (cerr << a << (--cnt ? ", " : ")\e[0m\n")));
}
template <typename I>
void orange_(const char *s, I L, I R) {
    cerr << "\e[1;32m[ " << s << " ] = [ ";
    for (int f = 0; L != R; ++L)
        cerr << (f++ ? ", " : "") << *L;
    cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

int ask(int x) {
    printf("? %d\n", x);
    fflush(stdout);
    int y;
    scanf("%d", &y);
    return y;
}

int main() {
    int n;
    scanf("%d", &n);
    
    if (ask(1) == 0) {
        printf("! 1\n");
        return 0;
    }
    int L_R = 1;
    int L = 1, R = n + 1;
    while (R - L > 1) {
        int M = (L + R) >> 1;
        int v = ask(M);
        if (v == L_R - 1) {
            --L_R;
            R = M;
        } else if (v == L_R) {
            printf("! %d\n", M);
            break;
        } else {
            ++L_R;
            L = M;
        }
    }
    return 0;
}