fix exercise not allowing zero as answer
fix exercise not allowing zero as answer

KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3,KhanovaSkola/khanovaskola-v3