The conditions on a Topological group

Question

I am familiar with group theory and topology. Now I am studying the concept of topological group. As per Munkres, it is defined as follows:

Let $G$ be a group together with a topology $\textit{T}$ defined on it. Then the topological space $(G,T)$ is said to be a topological group, if the following two functions

1. $G \times G \to G$, $(x,y) \mapsto xy$,
2. $G \to G$, $x \mapsto x^{−1}$

are continuous.

I can understand that the first condition gives a relationship between the binary operation defined on $G$ and the topology $T$. But I couldn't get why the second condition is necessary ? What will happen if we exclude the second condition ?