Consider these ten oxides: $\text{BeO}$, $\text{MgO}$, $\text{B}_2\text{O}_3$, $\text{Ga}_2\text{O}_3$, $\text{ZnO}$, $\text{SnO}_2$, $\text{CO}$, $\text{Cr}_2\text{O}_3$, $\text{CrO}_3$ and $\text{Mn}_2\text{O}_7$. Each oxide belongs to exactly one class: acidic, basic, amphoteric or neutral. Let $a$ be the number of amphoteric oxides and $b$ the number of acidic oxides in the list. What is the value of $10a + b$? The answer is an integer; give it exactly, with no rounding.