here is my input file:

# input for  ....find 17th and 18th number    

# input for  ....  again   
 
Nd  RES   PDB   val   
   1   140    31   20.0    
   1   142    33    0.0    
   1   143    34   10.0    
   1   144    35    0.0
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say 17th number is 143, would print out 10 on first loop then say 17th number is 140 would print 20 on second