#pragma GCC optimize(3, "Ofast", "inline")
#include <iostream>
#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#define INF 0x3f3f3f3f
#define L_INF 0x7f3f3f3f3f3f3f3f
#define db cout << "debug\n";

using namespace std;
const int Mod = 998244353;
using ll = long long;
const double pi = acos(-1);
void solve()
{
    int n;
    int m;
    cin >> n >> m;
    if (m == 1)
    {
        double ans = 0;
        for (int i = 1; i <= n; i++)
        {
            ans += 2 * i;
            for (int j = 1; j < i; j++)
            {
                double tmp = 0;
                tmp += 2 * (i - j) + 2 * j;
                tmp *= 2;
                ans += tmp;
            }
        }
            cout << fixed;
    cout << setprecision(10);
        cout << ans << '\n';
        return;
    }

    double ans = 0;
    for (int i = 1; i <= n; i++)
    {
        int div_pi = 2 * m / pi;
        // cout << div_pi << '\n';
        ans += pi * i * (1 + div_pi) * div_pi;
        ans += 4 * m * i * (m - div_pi);
        for (int j = 1; j < i; j++)
        {
            double tmp = (1 + div_pi) * div_pi * pi * j * 1.0 / (m * 1.0);
            tmp += (m - div_pi - 1) * 4 * j + 2 * j + 2 * m * (i - j);
            tmp *= 2 * m;
            ans += tmp;
        }
    }
    cout << fixed;
    cout << setprecision(10);
    cout << ans << '\n';
}
int main()
{
    IOS;
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
#ifndef ONLINE_JUDGE
    clock_t start_time = clock();
#endif
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
#ifndef ONLINE_JUDGE
    cout << "Used " << (double)(clock() - start_time) << " ms" << endl;
#endif
    return 0;
}