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The problem: a confused stack The task your system has to perform is to implement a stack of natural numbers. In general, the operations push, pop, and top should behave as normal for a stack, with the following exceptions: push() should not result in any change of the stack, except if the stack is empty, in which case it adds to the stack push(666) adds not just once 666 to the stack, but it adds it 3 times If the top element of the stack is 666, pop does not just remove it from the stack (and outputs it), it also removes the next element from the stack, without outputting it. If the top element of the stack is 666, top does not output 666, but 999. If the top of the stack is 7, pop does not remove it from the stack, but just outputs 7. If the top of the stack is 7, top does not output 7, it just removes it from the stack. push(3) does not add 3 to the stack, but instead 7. If the top of the stack is 319, then applying top outputs 666. push(13) first empties the stack (outputting each element in the sequence a series of pops would do) and then enters 13 on the stack If the top of the stack is 42, pop removes all elements of the stack, only outputting 42. Input file An input file consists of a sequence of push, pop and top commands, each command in its own line. Output file Each output from the program is written to the output file, followed by moving to a new line (so each element is in its own line). If the program encounters a command that is not push, pop or top, it outputs: Input error. and terminates. If the argument of a push command is not a natural number, it outputs: Imput error. and terminates. If the above does not say otherwise, performing top on an empty stack should result in an output of null and the program continues. Performing pop on an empty stack should result in the output Error and the program should terminate. O is not a natural number