#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main() {
    int a,b;double c;cin>>c>>a>>b;
    double v = 0.25*M_PI*M_PI*(a+b)*(b-a)*(b-a);
    cout << fixed <<setprecision(10) <<v*c <<endl;
    return 0;
}