#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<ll>> vvll;
const ll inf = 1e16;
const ll md = 1000000007;

int main() {
  double c,rin,rout;
  cin>>c>>rin>>rout;
  double r=(rout-rin)/2;
  double R=(rout+rin)/2;
  double ans=r*r*M_PI*2*M_PI*R*c;
  printf("%.7f",ans);
  return 0;
}