here's my code. I've tried many testes but i've passed them\

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

double f(double r, double a) {
        double rad=(a*4*atan((double)1))/180;
        double da=sqrt(
        2*r*r-2*r*r*cos(rad)
        );
        return da;
}

int main()
{
        double r,a,re,da,nr,rad;
        cin>>r>>a;
        re=r;
        nr=floor((double)180/a);
        da=f(r,2*a);
        re+=((nr-1)*da);
        double mod=360-floor(360/(2*a))*(2*a);
        //cout<<mod<<'\n';
        if(mod) re+=f(r,mod);
        cout<<fixed<<setprecision(6)<<re;
        return 0;
}