#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef double db;
#define V vector
#define pb push_back

const db PI = 2 * acos(0);

int main() {
    cout << fixed << setprecision(10);
    // cout << PI << endl;

    int n, m; cin >> n >> m;

    db ans2 = 0;
    if(m != 1) for(int i = 1; i <= n; i++) {
        ans2 += 2 * m * i;
    }

    // cout << ans2 << endl;

    auto dis_cycle = [&](int i, int j, int k) -> db {
        int dis = min((k - j + 2 * m) % (2 * m), (j - k + 2 * m) % (2 * m));
        db ans = 0;
        return min(i * 2 * PI * dis / (2 * m), (db)2 * i);
    };

    // cout << dis_cycle(1, 0, 2) << endl;

    for(int i = 1; i <= n; i++) {
        for(int k = 0; k < 2 * m; k++) {
            ans2 += 2 * m * dis_cycle(i, 0, k) * (n - i);
        }

        // cout << ans2 << endl;

        db tmp = 0;

        for(int k = 0; k < 2 * m; k++) {
            tmp += dis_cycle(i, 0, k) * 2 * m;
        }

        tmp /= 2;
        ans2 += tmp;
        // cout << ans2 << endl;

    }

    for(int i = 1; i <= n; i++) {
        for(int j = i + 1; j <= n; j++) {
            ans2 += 2 * m * 2 * m * (j - i);
        }
    }

    cout << ans2 << endl;
}