#include <bits/stdc++.h>
using namespace std;

typedef long long Int;
typedef pair<int,int> PII;
typedef vector<int> VInt;
 
#define FOR(i, a, b) for(i = (a); i < (b); ++i)
#define RFOR(i, a, b) for(i = (a) - 1; i >= (b); --i)
#define EACH(it, a) for(auto it = (a).begin(); it != (a).end(); ++it)
#define CLEAR(a, b) memset(a, b, sizeof(a))
#define SIZE(a) int((a).size())
#define ALL(a) (a).begin(),(a).end()
#define MP make_pair

void SolveTest(int test)
{
	int n, m;
	cin >> n >> m;
	int i, j;
	double pi = 2*acos(0.0);
	double sum = 0;
	FOR(i, 0, 2*m)
		sum += min(2.0, min(i, 2*m - i)*pi/m);

	double res = 0;
	FOR(i, 1, n + 1)
	{
		double r = sum*i;
		if(m > 1) res += i;
		res += r/2;
		FOR(j, i + 1, n + 1)
			res += r + 2*m*(j - i);
	}
	cout << fixed << setprecision(11) << res*2*m << endl;
}

int main()
{
	int T, t;
	T = 1;
	//cin >> T;
	FOR(t, 0, T) 
	{
		//cerr << "Solving " << t << "/" << T << endl;
		SolveTest(t);
	}

	return 0;
}