int cd2(char *number) {
    int i, d, total;
    total=0;
    for (i = 0; i<15; i++) {
        d=number[i]-48;
        if (!(i & 1)) {
            d *=2;
            if (d > 9) {d-=9;}
        }
        total+=d;
    }
    total *=9;
    return total % 10;
}