#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	double c;
	double Rin, Rout;
	cin >> c >> Rin >> Rout;
	double pi = 3.14159265358979; double hannkei = (Rout - Rin) / 2.0;
	double V = ((Rin + Rout) / 2.0) * 2 * pi * (hannkei * hannkei * pi);
	cout << fixed << setprecision(7) << V * c << endl;
	return 0;
}