Answer:

    PRINT "Enter the number of repeats"
    INPUT LIMIT

|   IF LIMIT < 0 THEN
|     PRINT "Number must be zero or greater"
|
|   ELSE
|
|     LET COUNT=1
| |   DO WHILE COUNT <= LIMIT
| | |   IF COUNT < LIMIT / 2 THEN
| | |     PRINT "Hello"
| | |   ELSE
| | |     PRINT "Mars"
| | |   END IF
| |
| |   LOOP
|     PRINT "Done"
|
|   END IF

    END

All the brackets are matched up, each bracket matches one of its own type, and inside brackets match inside brackets.