#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;



int main(){
  double PI = 3.14159265358979323846264338;
  int C;
  double Rin, Rout;
  cin >> C;
  cin >> Rin >> Rout;

  double A = ((Rout-Rin)/2.0);
  printf("%.9lf\n", (A * A * 2.0 * (Rout-A) * PI * PI)*C);
  return 0;
}