#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = long long;
using P = std::tuple<int,int>;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

double C, Rin, Rout;

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> C >> Rin >> Rout;

    double r1 = 1. * (Rin + Rout) / 2, r2 = 1. * (Rout - Rin) / 2;
    double pi = acos(-1);
    double res = 1. * C * 2 * pi * pi * r1 * r2 * r2;
    printf("%.10f\n", res);
}