String sentence;

String str$1,$ str$2,$ str$3$;

int length$1$;

sentence $=$ "First exam is on Monday.";

str$1=$ sentence.substring$(6,12)$;

str$2=$ str$1.$substring$(0,4)$;

str$3=$ sentence.replace$(\text{'}$i$\text{'},\text{'}$#$\text{'})$;

length$1=$ sentence.length$()$;

Based on the code above, what is the value of length$1?$