#include <bits/stdc++.h>   using namespace std;   const int N = 100010;   void answer(int u) {     printf( ! %d n , u);     fflush(stdout);   }   int ask(int u) {     printf( ? %d n , u);     fflush(stdout);     int res;     scanf( %d , &res);     return res;   }   bool inside(int u, pair<int, int> v) {     return ((u > v.first) ^ (u >= v.second)) == 1;   }   bool check(pair<int, int> u, pair<int, int> v) {     if (inside(u.first, v) && inside(u.second, v)) {       return 1;     }     if (inside(v.first, u) && inside(v.second, u)) {       return 1;     }     if (inside(u.first, v) && inside(v.first, u)) {       return 1;     }     if (inside(u.second, v) && inside(v.second, u)) {       return 1;     }     return 0;   }   int main() {     int n;     scanf( %d , &n);     if ((n / 2) % 2 != 0) {       answer(-1);       return 0;     }     int x = ask(1);     int y = ask(1 + n / 2);     if (x == y) {       answer(1);       return 0;     }     pair<int, int> u(x, y);     pair<int, int> v(y, x);     int low = 1, high = n / 2 + 1;     while (high - low > 1) {       int mid = (high + low) / 2;       int foo = ask(mid);       int bar = ask(mid + n / 2);       if (foo == bar) {         answer(mid);         return 0;       }       pair<int, int> a(u.first, foo);       pair<int, int> b(v.first, bar);       if (check(a, b)) {         high = mid;         u = a;         v = b;       } else {         low = mid;         u = make_pair(foo, u.second);         v = make_pair(bar, v.second);       }     }     answer(low);     return 0;   }   