#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  double C,a,b;
  cin>>C>>a>>b;
  double pi = 3.1415926535;
  cout<<fixed<<setprecision(15)<<C*(a+b)*pi*((b-a)/2)*((b-a)/2)*pi<<endl;
}