#include <iostream>
#include <iomanip>
using namespace std;
 
int main(){
    int C, Rin, Rout;
    cin >> C >> Rin >> Rout;
    cout << setprecision(17) << (Rout - Rin) * (Rout - Rin) * (Rout + Rin) * 3.1415926535 * 3.1415926535 / 4 * C << endl;
}