#include <iostream>
#include<math.h>

int main()
{
    double A,B,H,M;
    double r;
    std::cin>>A>>B>>H>>M;
    H=(H*60+M)*.5;
    H > M*6 ? r = H - M*6 : r = M*6 - H;
    if(r>180)
    {
        r=360-r;
    }
    if(r==0)
    {
        std::cout<< 0 << std::endl;
        return 0;
    }

    r = (r  * M_PI)/ 180.0;
    std::cout<<sqrt((double)(A*A+B*B)-(double)(2*A*B)*(double)cos(r))) << endl;;
    return 0;
}
