#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vec;
typedef vector<string> vecstr;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define NO printf("NO")
#define YES printf("YES")

int main() {
    double c;
    cin >> c;
    double rin, rout;
    cin >> rin >> rout;

    double pi = 3.14159265358979;

    double r = (rout - rin) / (double)2;
    double s = r * r * pi;
    double l = (rin + r) * (double)2 * pi;
    double v = s * l;
    double ans = v * c;
    cout << ans << endl;
}