#include <stdio.h>

int main() {
    int n, ans, st, dr, mij;

    scanf( "%d", &n );

    st = 0;
    dr = n;
    while ( dr - st > 1 ) {
        mij = (st + dr) / 2;

        printf( "? %d\n", mij );
        fflush( stdout );
        scanf( "%d", &ans );

        if ( ans == 1 )
            dr = mij;
        else
            st = mij;
    }

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

    return 0;
}