#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef __float128 db;

const db Pi = acos(-1.);

int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	cout << fixed << setprecision(15);
	LL n, m;
	cin >> n >> m;
	if(n == 0 || m == 0)
	{
		cout << "0\n";
		return 0;
	}
	
	db ans = 0;
	FOR(dR, 0, m + 1)
	{
		db kut = dR * Pi / m;
		//cerr << kut << endl;
		
		db ml = 2 * m;
		if(dR == m)
			ml = m;
		
		if(kut > 2)
		{
			ans += ml * n * n * (n + 1);
		}
		else
		{
			FOR(R, 1, n + 1)
			{
				ans += ml * kut * R * (2 * (n - R) + 1);
				
				if(dR == 0)
					ans += ml * (n - R) * R;
				else
					ans += ml * 2 * (n - R) * R;
			}
		}
	}
	if(m != 1)
		ans += m * n * (n + 1);
	
	
	cout << (long double)ans << "\n";
	
	
	return 0;
}