#include <functional>
#include <algorithm>
#include <iostream>
#include <utility>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cstring>
#include <vector>
#include <cstdio>
#include <string>
#include <stack>
#include <deque>
#include <queue>
#include <cmath>
#include <map>
#include <set>
//#include <bits/stdc++.h>
//#define pb push_back
//#define pf push_front
//#define ppb pop_back
//#define ppf pop_front
#define lwb lower_bound
#define upb upper_bound
#define X first
#define Y second
//#define FOR(i,j,k) for(int i = j; i < (int)(k); i++)
//#define FORV(i, v) FOR(i, 0, ((v).size()))
//#define sz(a) (int)((a).size())
//#define all(a) a.begin() , a.end()
#define coud(a,b) cout<<fixed << setprecision((b)) << (a)
#define L(x) ((x)<<1)
#define R(x) (((x)<<1)+1)
//#define int long long
#define double long double
#define joon ios :: sync_with_stdio(false)
//#define cin fin
//#define cout fout

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const double pi = acos(-1);
const double eps = 1e-7;

int main()
{
	joon;
	cin.tie(0);

	double a,r;
	cin>>a>>r;
	double tet=a/(2*r);
	tet=asin(tet)*180.0/pi;
	tet*=2;
	double s=pi*r*r;
	s*=tet/360.0;
	double r2=r;
	r2*=r2;
	double bh=a/2.0;
	bh*=bh;
	r2-=bh;
	double oh=(double)sqrt(r2);
	oh*=a;
	oh/=2.0;
	s-=oh;
	cout<< fixed << setprecision(12) << s << endl;

	return 0;
}