#include <bits/stdc++.h>
using namespace std;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

const double pi = 3.14159265358979323;

int main(){
    int c,Rin,Rout;
    cin >> c >> Rin >> Rout;

    double r = (Rout-Rin)/2.0;
    double r2 = r + Rin;
    double res = pi*r*r*r2*2*pi*c;

    printf("%.16f\n", res);
    return 0;
}