#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <utility>
#include <list>
#include <queue>
#include <map>
#include <iterator>
#include <iomanip>
#include <complex>
using namespace std;

using ull = unsigned long long;
using ll = long long;


int main()
{
    double c,r1,r2;
    cin >> c >> r1 >> r2;

    cout << fixed << setprecision(10) <<c*((r2-r1)/2)*((r2-r1)/2)*M_PI*(r1+r2)*M_PI << endl;
}