#include<iostream>
#include<string>
#include<algorithm>
#include<cmath>
#include<iomanip>
#include<cstring>
#include<map>
#include<vector>
#include<queue>
#include<utility>
using namespace std;
typedef long long int ll;

int main(){

  double c, rin, rout;
  cin >> c >> rin >> rout;

  double R=(rout+rin)/2;
  double r=rout-R;
  double ans=c*pow(r, 2)*pow(M_PI, 2)*2*R;
  cout << fixed << setprecision(10) << ans << endl;

  return 0;
}