#include<iostream>
#include<stdio.h>
#include<vector>
#include<algorithm>

#define PI 3.141592

using namespace std;

int main(){

    int c, ri, ro;
    cin>> c;
    cin>> ri>> ro;

    double r = (ro-ri)/2.0;
    double vol = PI*(ri+ro)*PI*r*r;

    printf("%.4f\n", vol*c);
    return 0;
}