#include using namespace std; using uint = unsigned int; using ll = long long; using ull = unsigned long long; template using V = vector; template using VV = V>; template using VVV = V>; template using VVVV = VV>; #define rep(i,n) for(ll i=0ll;i void chmin(T& t, const U& u) { if (t > u) t = u; } template void chmax(T& t, const U& u) { if (t < u) t = u; } // cin.tie(nullptr); // ios::sync_with_stdio(false); // cout << fixed << setprecision(20); void solve(){ ll c,a,b; cin >> c >> a >> b; double ans = 2.0*M_PI*M_PI; ans *= (b-a)*(b-a); ans *= (a+b); ans /= 8; cout << fixed << setprecision(20); cout << ans << endl; } int main(){ cin.tie(nullptr); ios::sync_with_stdio(false); int t=1; // cin >> t; rep(i,t) solve(); }