#include <math.h>
#include "iostream"
#include "algorithm"
using namespace std;

int main() {
    int i,j,k=0;
    double c, in, out = 0.0;
    cin >> c;
    cin>>in>>out;

    printf("%.14f\n", ((out-in)/2.0+ in) * 2.0 * M_PI * (out-in)/2.0 * (out-in)/2.0 * M_PI * c);

    return 0;
}