#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    double pi = acos(-1);
    int c, a, b;
    cin>>c>>a>>b;
    double r = (b-a)/2.0;
    cout << pi * r * r * (a+b) * pi * c << endl;
    return 0;
}