#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    int c,in,out;
    cin>>c>>in>>out;
    //公式：π × π ÷ 4 × ( a + b ) × ( b - a ) × ( b - a )
    double result = c*M_PI*M_PI/4*(in+out)*(out-in)*(out-in);
    printf("%f\n", result);
    return 0;
}