#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }


using Double = long double;

struct Pt {
	Double x, y;
	Pt() {}
	Pt(Double x, Double y) : x(x), y(y) {}
	Pt operator+(const Pt &a) const { return Pt(x + a.x, y + a.y); }
	Pt operator-(const Pt &a) const { return Pt(x - a.x, y - a.y); }
	Pt operator*(const Pt &a) const { return Pt(x * a.x - y * a.y, x * a.y + y * a.x); }
	Pt operator/(const Pt &a) const { const Double d2 = a.abs2(); return Pt((x * a.x + y * a.y) / d2, (y * a.x - x * a.y) / d2); }
	Pt operator+() const { return Pt(+x, +y); }
	Pt operator-() const { return Pt(-x, -y); }
	Pt operator*(const Double &k) const { return Pt(x * k, y * k); }
	Pt operator/(const Double &k) const { return Pt(x / k, y / k); }
	friend Pt operator*(const Double &k, const Pt &a) { return Pt(k * a.x, k * a.y); }
	Pt &operator+=(const Pt &a) { x += a.x; y += a.y; return *this; }
	Pt &operator-=(const Pt &a) { x -= a.x; y -= a.y; return *this; }
	Pt &operator*=(const Pt &a) { return *this = *this * a; }
	Pt &operator/=(const Pt &a) { return *this = *this / a; }
	Pt &operator*=(const Double &k) { x *= k; y *= k; return *this; }
	Pt &operator/=(const Double &k) { x /= k; y /= k; return *this; }
	Double abs() const { return sqrt(x * x + y * y); }
	Double abs2() const { return x * x + y * y; }
	Double arg() const { return atan2(y, x); }
	Double dot(const Pt &a) const { return x * a.x + y * a.y; }
	Double det(const Pt &a) const { return x * a.y - y * a.x; }
	friend ostream &operator<<(ostream &os, const Pt &a) { os << "(" << a.x << ", " << a.y << ")"; return os; }
};
const Double EPS = 1e-10;
const Double INF = 1e+10;
const Double PI = acos(-1.0);
inline int sig(Double r) { return (r < -EPS) ? -1 : (r > +EPS) ? +1 : 0; }
inline Double tri(const Pt &a, const Pt &b, const Pt &c) { return (b - a).det(c - a); }

double aCC(Pt a, double r, Pt b, double s) {
	double d = (a - b).abs();
	if (sig(r - s - d) >= 0) return s * s * PI;
	if (sig(s - r - d) >= 0) return r * r * PI;
	if (sig(r + s - d) <= 0) return 0;
	double x = (d * d + r * r - s * s) / (d * 2);
	double h = sqrt(r * r - x * x);
	return r * r * atan2(h, x) + s * s * atan2(h, d - x) - d * h;
}


constexpr int N = 1'000'000;

Double R, H, D;

int main() {
  for (; ~scanf("%Lf%Lf%LF", &R, &H, &D); ) {
    Double ans = 0.0L;
    for (int i = 0; i <= N; ++i) {
      const Double r = R / N * i;
      const Double res = aCC(Pt(0.0L, 0.0L), r, Pt(D, 0.0L), r);
      ans += ((i == 0 || i == N) ? 1 : (i % 2 == 0) ? 2 : 4) * res;
    }
    ans *= (H / N) / 3.0L;
    printf("%.12Lf\n", ans);
  }
  return 0;
}