#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <cctype>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <list>
#include <stdio.h>
#include <string.h>
#include <cstdlib>
#include <math.h>
#include <bitset>
#include <iterator>
#include <iomanip>
#include <sstream>
#include <numeric>
#define INF 2000000000
using namespace std;
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
int gcd(int a,int b){if(a%b==0){return b;}else return gcd(b,a%b);}
int lcm(int a,int b){if(a==0){return b;} return a/gcd(a,b)*b;}
int MOD; template<class T> void mod(T &n){MOD=n;}
#define sym cout<<"---------"<<endl;
#define ll long long
#define PL pair<long long, long long>
#define P pair<int,int>
#define mk make_pair
#define en endl
#define WHITE 0
#define BLACK 2
#define GRAY 1
#define RE return 0
#define int ll

double pi=3.141592;

signed main(){
  cout<<fixed; cout<<setprecision(5);
  double c,rin,rout;
  cin>>c>>rin>>rout;
  double r=(rout-rin)/2;
  double ans=c*r*r*pi*2*(rin+r)*pi;
  cout<<ans<<en;
}