#include<cstdio>
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
using namespace std;

typedef long long LL;
typedef vector<int> VI;


const double PI = M_PI;
double C, Rin, Rout;
int main() {
    cin >> C >> Rin >> Rout;
    double r = (Rout - Rin) / 2.0;
    double S = r * r * PI;
    double R = (Rin + Rout) / 2.0;
    double V = 2 * PI * R * S;
    printf("%.6f\n", V*C);
    return 0;
}