#include <iostream>
#include<iomanip>
#include <cmath>
using namespace std;
typedef signed long long ll;
 
#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i,s,n) for (int i = (s); i < (n); i++)
#define RFOR(i,s,n) for (int i = (n)-1; i >= (s); i--)
 
 
int main() {
	long double C,Rin,Rout;
	
	
	cin >> C;
	cin >> Rin >> Rout;
	
	long double poi = (pow(M_PI,2)/4)*(Rout+Rin)*(pow(Rout-Rin,2))*C;
	
	cout << fixed << setprecision(10) << poi << endl;
 
	return 0;
}