Add missing semicolon

chapter01.tex

@@ -328,7 +328,7 @@ For example, the following code calculates $n!$,
 the factorial of $n$, modulo $m$:
 \begin{lstlisting}
 long long x = 1;
-for (int i = 2; i <= n i++) {
+for (int i = 2; i <= n; i++) {
     x = (x*i)%m;
 }
 cout << x%m << "\n";