Started problem 16
Completed problem 16
Merge branch 'problem/16' into develop
Started problem 17
Completed problem 17
Merge branch 'problem/17' into develop
Started problem 18
Completed problem 18
Merge branch 'problem/18' into develop
Started and completed problem 67
Merge branch 'problem/67' into develop
Started problem 19
Completed problem 19
Merge branch 'problem/19' into develop
Started problem 20
Completed problem 20
Merge branch 'problem/20' into develop
Started problem 21
Completed problem 21
Merge branch 'problem/21' into develop