Problem Statement  
All numbers between 1 and N, inclusive, in ascending order and with no spaces in between, were written on a piece of paper. Afterwards, some of the digits were erased. You will be given a String[] leftDigits. Concatenate all the elements of leftDigits, and the resulting string will contain the digits that are left on the piece of paper, in order. Return the lowest possible value that N could have had.  
Definition  
 
Constraints  
  leftDigits will contain between 1 and 50 elements, inclusive.  
  Each element of leftDigits will contain between 1 and 50 characters, inclusive.  
  Each character in leftDigits will be a digit ('0''9').  
Examples  
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