Special Round off 1

Statement: You are given an integer n and a count c. Integer n can consists of all digits from 0 to 9. You have to sum up last c digits of integer until it becomes a single digit value (0 <= d <= 9) and have to perform the following operations: 1) If the sum of last c digits is greater than equal to 5 and less than equal to 9 (5 <= sum <=9), then replace all the last c digits with a single d