#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define maxn 1000
#define ld double
double cir[maxn], sum[maxn];
const ld Pi = acos(-1);
ld min_ld(ld a, ld b) {
	return (a < b) ? a : b;
}
void solve(){
	double n, m;
	cin >> n>> m;
	
	ld ans = 0;
	if(m != 1) ans += (n * (n + 1) * m);
	ld avg_angle = Pi / (1.0 * m);
	
	for (int i = 1;i <= n;i ++){
		for (int j = 1;j < m;j ++){
			ld cir_dis =  j * 1.0 * avg_angle;
			cir[i] += min_ld(cir_dis * i, 2.0 * i);			
		}
		cir[i] *= 2.0;
		cir[i] += 2.0 * i;
		ans += (cir[i] * 1.0 * m);
		ans += (sum[i - 1] + (i - 1) * 2.0 * m) * 2.0 * m;
		sum[i] = sum[i - 1] + (i - 1) *2.0* m + cir[i];
	}
	printf("%.10lf", ans);
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	// cout << setiosflags(ios::fixed)<<setprecision(10);
	int T = 1;
	// cin >> T;
	while (T --)
		solve();
}