#include<bits/stdc++.h>
#define int long long
#define db long double
using namespace std;

const db pie = acos(0.50) * 3.0;

int n, m, k;
struct node{
	int fi, se;
	node operator + (const node &p) const{ return {fi + p.fi, se + p.se}; }
	node operator * (const int &p) const{ return {fi * p, se * p}; }
}ans;

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	cin >> n >> m; int k = 2.0 * (db)m / pie;
	if(m == 1) return cout << fixed << setprecision(10) << n * (2 * n + 1) * (2 * n + 2) / 3 - n * (n + 1), 0;
	ans = {n * (n + 1) * m, 0};
	node val = {2 * m * (2 * m - 2 * k - 1), k * (k + 1)};
	ans = ans + (val * (n * (n + 1) / 2));
	val = val * 2; node res = val;
	for(int i = 1; i < n; ++i){
		ans = ans + (res * (n - i));
		ans.fi += (n - i) * (n - i + 1) * 2 * m * m;
		res = res + val;
	}
	cout << fixed << setprecision(10) << ans.se * pie + ans.fi;
	
	return 0;
}