#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define LL __int128
#define fi first
#define se second
#define int __int128
using namespace std;

const int inf = 1e9;
const ll Inf = 1e18;
const double pie = acos(-1);
ll n, m;
struct node{
	long double x, y;
	node(){x = y = 0;}
}sum, ans;

node operator + (node x, node y){
	node z;
	z.x = (x.x + y.x);
	z.y = (x.y + y.y);
	return z;
}

node operator * (node x, int y){
	node z;
	z.x = x.x * y;
	z.y = x.y * y;
	return z;
}

int qpow(int x, int y){
	int sum = 1;
	while(y){
		if(y & 1) sum = 1ll * sum * x;
		x = 1ll * x * x;
		y >>= 1;
	}
	return sum;
} 

ll calc(int x){return x * (x + 1) / 2;}

signed main(){
//	freopen("a.in", "r", stdin);
//	freopen("a.out", "w", stdout);
    ios::sync_with_stdio(false);
    cout.tie(0);
    cin.tie(0);
    
    cin >> n >> m;
//    int invm = qpow(m, mod - 2, mod);
    int k = 2.0 * m / pie;
    for(int i = 1; i <= n; i++){
    	node s;
    	int x = calc(k);
    	x = x * i * 2;
    	int y = 4 * (m - k - 1) * m * i + 2 * i * m;
    	s.x = x; s.y = y;
    	node ss = s; ss.x /= m; ss.y /= m;
    	sum.y += (i - 1) * m * 2 + 1;
    	ans = ans + s + sum * m * 2;
	    sum = sum + ss;
	}
	if(m == 1) return printf("%.9lf", (double)(ans.x * pie + ans.y - n * (n + 1))), 0;
	printf("%.9lf", (double)(ans.x * pie + ans.y));
	
    return 0;
}