#include <stdio.h>

int main()
{
    int n;
    scanf("%d", &n);

    int guess = 0;
    int step = (1 << 30);
    for(; step > 0; step /= 2)
    {
        int nguess = guess + step;
        if(nguess > n)
            continue;

        printf("? %d\n", nguess);
        fflush(stdout);

        int answer;
        scanf("%d", &answer);

        if(answer == 0)
            guess = nguess;
    }

    printf("! %d\n", guess);
    fflush(stdout);

    return 0;
}