#include <iostream>
#include <math.h>
#include <algorithm>
#include <functional>
#include <vector>
#include <typeinfo>
#include <climits>
#include <ctype.h>
#include <string>
#include <stack>
#include <bits/stdc++.h>
using namespace std;
#define FOR(i, a, n) for (int i = a; i < n; i++)
#define REP(i, n) for(int i = 0; i < n; i++)
struct omt{omt(){ios::sync_with_stdio(false);cin.tie(0);}}star;

int main(){
    double c, a, b;
    cin >> c >> a >> b;
    c = double(c);

    double v;
    v = (pow(M_PI, 2) * (a + b) * pow((a - b), 2)) / 4.0;
    
    cout << fixed << setprecision(6);
    cout << c * v << endl;


    return 0;
}