#include <bits/stdc++.h>
using namespace std;
#define mp make_pair
#define e1 first
#define e2 second
#define pb push_back
typedef pair <int, int> PII;
typedef unsigned int ui;
typedef unsigned long long int ull;
typedef long long int ll;
typedef long double ld;
typedef pair <int, ll> PIL;
typedef pair <ll, int> PLI;
typedef pair <ll, ll> PLL;
const int mod = 1e9+7;
const int inf = 1e9+9;
const ll MOD = 1e9+696969;
const ll INF = ll(1e18) + 3;
const ld PI = 3.1415926535897932;


ld a, r;
ld WYNALL;
ld todegree(ld a)
{
    return a * (180.0 / PI);
}
void F(ld a, ld r)
{
    ld apol = a * 0.5;
    ld pole = PI * r * r;
    ld katrad = asin(a / (2 * r) );
    ld katdeg = todegree(katrad) * 2;
    ld wyn = (katdeg / 360) * pole;
    ld H = sqrt(r*r - apol * apol);
    wyn -= (apol * H);
    WYNALL += wyn;
}
int main()
{
    ld r1, r2;
    cin >> a >> r1 >> r2;
    F(a, r1); F(a, r2);
    cout << fixed;
    cout << setprecision(15);
    cout << WYNALL;
}