Problem Statement  
In order to sharpen their basic arithmetic skills, kids often try to represent numbers using match sticks. As one is only given a limited number, one student is curious how high he can count with his matches.
Each one digit number is represented as follows:  number 8 uses seven matches.  numbers 0, 6 and 9 each use six matches.  numbers 2, 3 and 5 each use five matches.  numbers 4 and 7 each use four matches.  number 1 uses two matches. Given an int n denoting the number of matches he has at his disposal, return the smallest positive integer that cannot be represented.  
Definition  
 
Constraints  
  n is between 1 and 128, inclusive.  
Examples  
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