#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main(){
   double c,ri,ro;
   cin >> c >> ri >> ro;
   cout << fixed << setprecision(10) << (ro - ri) / 2 * (ro - ri) / 2 * 2 * M_PI * M_PI * (ri + ro) / 2 * c << endl;
}