int simple() {
    int r = (rand() % 100 + 3) | 1;
    bool b = true;
    while (b) {
        for (int i = 3; i*i < r; i = i + 2) {
            if (r % i == 0){
                b = false;
                break;
            }
        }
        if (!b) {
            r += 2;
            b = true;
        }
        return r;
    }
    return 1;
}