#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef pair<int,int> P;
 
const int INF = 1e9;
const int mod = 1e9+7;
const double EPS = 1e-10;
const double PI = acos(-1.0);
 
int main()
{
    int c,in,out;
    cin >> c >> in >> out;
    double r = (out-in)/2.0;
    cout << fixed << c*r*r*PI*2*PI*(r+in) << endl;
    return 0;
}