Standard input is empty

 0
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
 0
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
 0
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
 0
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3
     1
         2
             3
         2
             3