#include <stdio.h>


int main() {
    FILE *fin, *fout;
    fin = fopen("cbinteractiv.in", "r");
    fout = fopen("cbinteractiv.out", "w");
    
    int n, st, dr, mijl, rasp;
    
    scanf("%d", &n);
    
    st = 0;
    dr = n;
    while (dr-st>1) {
        mijl = (st+dr)/2;
        printf("? %d", mijl);
        fflush(stdout);
        printf("\n");
        scanf("%d", &rasp);
        if (rasp==0) {
            dr = mijl;
        } else {
            st = mijl;
        }
    }
    
    printf("! %d", st);

    fclose(fin);
    fclose(fout);
    return 0;
}