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

int main() {
    double pi = 3.14159265359,i,o,ans,r,c;
    cin >> c >> i >> o;
    r = (o-i)/2;
    ans = pi*2*(i+r)*r*r*pi*c;
    printf("%f",ans);
    return 0;
}