#include <cstdio>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")
int main() {
    int N;
    scanf("%d", &N);
    int st = 1, dr = N, mid;
    while(st <= dr) {
        mid = (st + dr) >> 1;
        printf("? %d\n", mid);
        fflush(stdout);
        int ans;
        scanf("%d", &ans);
        if(ans == 0) {
            st = mid + 1;
        } else if(ans == 1) {
            dr = mid - 1;
        } else {
            return 0;
        }
    }
    printf("! %d\n", st);
    return 0;
}