#include<cstdio>
#include<cstring>
#include<cctype>
#include<cmath>
#include<climits>
#include<algorithm>
#include<vector>
#include<valarray>
#include<string>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<iostream>
using namespace std;
  
  
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<=n;i++)
#define drep(i,n) for(int i=n-1;i>=0;i--)
#define DREP(i,n) for(int i=n;i>0;i--)
#define Rep(i,m,n) for(int i=m;i<n;i++)
#define ReP(i,m,n) for(int i=m;i<=n;i++)
#define scani(a) scanf("%d",&a)
#define scand(a) scanf("%lf",&a)
#define scans(s) scanf("%s",s)
#define readi(a) int a;scanf("%d",&a)
#define printi(a) printf("%d",a)
#define prints(s) printf("%s",s)
#define even(n) (((n)+1)%2)
#define odd(n) ((n)%2)
#define sg(x) ((x)?1:0)
#define LF printf("\n")
#define SPACE printf(" ")
#define pb push_back
#define mp make_pair
#define bs binary_search
#define all(a) (a).begin(),(a).end()
#define forall(itr,a) for(auto itr=a.begin();itr!=a.end();++itr)
#define MOD 1000000007
  
typedef long long LL;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef pair<double,double> pdd;
typedef pair<int,int> pii;
  
const double pi=acos(-1.0);
double rad(double t){return t*pi/180.0;}
double deg(double d){return d*180.0/pi;}
int GCD(int x,int y){if(x<y)swap(x,y);return x%y?GCD(y,x%y):y;}
int LCM(int x,int y){return x/GCD(x,y)*y;}


int main(){
  double C,Rin,Rout;
  cin >> C >> Rin >> Rout;
  double R=(Rout+Rin)/2.0;
  double r=(Rout-Rin)/2.0;
  printf("%.6lf\n",2*pi*pi*r*r*R*C);
  return 0;
}