#include <stdio.h>
int n;
int main(int argc, char const *argv[]) {

  int n;
  scanf("%d", &n);
  int lo = 1, hi = n, ans = -1;

  while(lo<hi) {
    int m = (lo+hi)/2;
    printf("? %d\n", m);
    fflush(stdout);
    int q;
    scanf("%d", &q);
    if(q == 0) lo = m + 1;
    else if(q == 1) hi = m;
    else return 0;
  }
  printf("!%d", lo);

  return 0;
}