# include <bits/stdc++.h>

const int32_t maxn = 10000005;

int64_t n, m, p, s;

struct node {
	// int64_t 
	
	long double x, y;
	
	inline node operator * (const int64_t & a) const {
		return {x * a, y * a};
	}
	
	inline node operator + (const node & a) const {
		return {(x + a.x), (y + a.y)};
	}
	
} pre, suf, ans;

inline int64_t sm (const int64_t x) {
	return x * (x + 1) / 2;
}

struct frac {
	long double x, y;
	
	inline bool operator < (const frac & a) const {
		return x * a.y < y * a.x;
	}
} f[maxn], pi;

int main () {
	
	std::cin >> n >> m, p = 2 * m;
	
	if (n == m && n == 1)
		return std::cout << std::fixed << std::setprecision (10) << 2 << '\n', 0;
	
	for (s = 1; s <= m; ++ s) 
		if (s * acos (- 1) > 2.0 * m)
			break ;
	
	-- s;
	
	for (int i = 1; i <= n; ++ i) {
		
		node mid = {sm (s) * 2.0 * i / m, (2.0 * m - 1 - 2 * s) * 2 * i};
		
		node inc = pre + (node) {0, sm (i - 1) * 2.0 * m};
		
		pre = pre + mid, ans = ans + (mid + inc * 2) * 2 * m;
	
	}
	
	if (m != 1)
		ans = ans + (node) {0, sm (n) * 4.0 * m}; 
	
	std::cout << std::fixed << std::setprecision (10) << ans.x / 2.0 * acos (- 1) + ans.y / 2.0 << '\n';
	
	return 0;
}