#define _USE_MATH_DEFINES
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
    int a,x,y;cin>>a>>x>>y;
    cout << fixed << setprecision(15) << (double)(a*(2*((y-x)/2)*((y-x)/2)*((y+x)/2)*M_PI)) << endl;
    
}