double f2(){
    double undersqrt = sqr(L)*sqr(v0)(g*sqr(L)*(-H+p) + 4*H*(H+p)*sqr(v0));
    if(undersqrt < 0){return -1;}
    return (4*H*L*sqr(v0)-sqrt(2*undersqrt))/(g*sqr(L)+4*H*sqr(v0));
}