#define _USE_MATH_DEFINES
#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<string>
#include<vector>
#include<queue>
#include<utility>
#include<set>
#include<map>
#include<cctype>
#include<cmath>
#include<algorithm>
using namespace std;

#define RALL(x) (x).rbegin(),(x).rend()
#define ALL(x) (x).begin(),(x).end()
#define repp(i,n) for(int (i)=1;(i)<=(n);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define EACH(itr,c) for(__typeof((c).begin()) itr=(c).begin(); itr!=(c).end(); itr++)
#define clr(a) memset((a), 0 ,sizeof(a))

typedef pair<int,int> P;
typedef vector<pair<int,int> > pii;
typedef map<int,int> mi;


int main(){
	double a,b,c;
	cin >> a >> b >> c;
	double B=c-(c-b)/2;
	double C=(c-b)/2;
	printf("%.6lf\n",pow(C,2.0)*B*pow(M_PI,2.0)*2*a);
	return 0;
}