#include <iostream>
#define lol long long

int main()
{
    int n;
    scanf("%d", &n);
    lol biggest = n;
    lol smallest = 1;
    while (smallest < biggest)
    {
        lol mid = (biggest + smallest) / 2;
        printf("? %lld\n", mid);
        fflush(stdout);
        int rez;
        scanf("%d", &rez);
        if (rez == 0)
            smallest = mid + 1;
        else
            biggest = mid;
    }
    printf("! %lld\n", smallest);
    fflush(stdout);
}