#include <bits/stdc++.h>

#define rep(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int C;
    int Rin, Rout;
    cin >> C;
    cin >> Rin >> Rout;
    double r = Rout-Rin;
    r /= 2;
    double ans = C*r*r*M_PI * M_PI*(Rout+Rin);
    printf("%.15lf\n", ans);
    return 0;
}