#include <bits/stdc++.h>
using namespace std;
using LD = long double;
constexpr LD PI = acosl(-1.0L);

constexpr LD eps = 1e-9;
int sgn(LD x) {return fabs(x)<=eps ? 0 : (x>eps ? 1 : -1);}

int main() {
    std::ios::sync_with_stdio(false); cin.tie(0);
    cout << setiosflags(ios::fixed) << setprecision(10);

    int n, m;
    cin >> n >> m;
    LD ans = 0;
    LD th = PI / m;

    if (m>1) {
        for (int r1=1; r1<=n; ++r1) {
            ans += 2*m*r1;
        }
    }
    // printf("ans=%Lf\n", ans);

    for (int r1=1; r1<=n; ++r1) {
        LD res = 0.0L;
        int cnt = 0;
        LD arc = 0.0L;
        for (int i=1; sgn(i*th-2) < 0; ++i) {
            arc += th*i*r1;
            ++cnt;
        } 
        LD tmp = arc*2 + (((m-cnt)*2-1)*r1*2);
        // printf("tmp=%Lf\n", tmp);
        res += tmp / 2;
        for (int r2=r1+1; r2<=n; ++r2) {
            res += (r2-r1)*2*m + tmp;
        }
        res *= 2*m;
        ans += res;
    }

    cout << ans << '\n';
    return 0;
}