#include using namespace std; using ll = long long; int main(){ ios::sync_with_stdio(false); cin.tie(0); double a, b, ans = 0, cnt = 0; cin >> a >> b; for(double i = a; i <= b; i += 0.00000001){ ans += 1 - abs(i); cnt++; } ans *= 4 * M_PI * (b - a) / cnt; cout << fixed << setprecision(15) << ans << '\n'; }