#include<iostream>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<algorithm>
#include<vector>
#include<math.h>
#include<iomanip>
#include<stack>
#include<queue>
#include<set>
#include<map>

using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;

//const ll mod = 1000000007;
const ll mod = 998244353;
const double pi = 3.14159265358979;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(15);
	double c , ri , ro;
	cin >> c >> ri >> ro;
	double a = (ro - ri) / 2;
	double b = ri + a;
	double ans = a * a * b * 2 * pi * pi * c;
	cout << ans << endl;
	return 0;
}