#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
#define mems(x, v) memset(x, v, sizeof x)
#define mcpy(x, y) memcpy(x, y, sizeof x)
using namespace std;
typedef pair <int, int> pii;
typedef long long ll;
typedef unsigned long long ull;
typedef long double wisdom;

const double PI = acos(-1);
int main() {
	//freopen("a.in", "r", stdin); freopen("a.out", "w", stdout);
	int n, m, lim = 0; double ans = 0; cin >> n >> m;
	if (m == 1) {
		for (int i = -n; i <= n; i++) ans += ((n - i + 1) * (n - i) / 2.0 - abs(i));
		return printf("%.10lf", ans), 0;
	}

	for (int i = 1; i <= n; i++) ans += 2 * m * i;
	for (int i = 1; i < m; i++) if (i * PI < 2 * m) lim = i;
	for (int x = 1; x <= n; x++) {
		double tDO = x * lim * (lim + 1)/ 2.0;
		double tVA = x + 2.0 * x * (m - lim - 1);

		tDO *= 2, tVA *= 2 * m;
		ans += PI * (tDO + 2 * tDO * (n - x));
		ans += (tVA + 2 * tVA * (n - x));
		ans += (n - x) * (n - x + 1.0) / 2 * 4 * m * m;
	}
	printf("%.10lf", ans);
	return 0;
}