#include <bits/stdc++.h>
using namespace std;
#define REP(i,N) for(int i=0;i<N;i++)
int main(){
	int C,Rin,Rout;
	double A,B;
	
	cin>>C>>Rin>>Rout;
	A=M_PI*(Rout-Rin)*(Rout-Rin)/4.0;
	B=2*M_PI*(Rout+Rin)/2.0;
	cout<<fixed<<C*A*B<<endl;
	
	return 0;
}