#include <bits/stdc++.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

string ban[2] = {"oda", "yukiko"};

#define SQ(x) ((x)*(x))

int main() {
  
  int C; cin >> C;
  int R1, R2 ; cin >> R1 >> R2;
  double X = (R2-R1)/2.;
  printf("%.8f\n", SQ(X)*M_PI * 2*(R2-X)*M_PI * C);
  
  return 0;
}