```
java -cp out:out_private ru.fizteh.fivt.students.dsalnikov.calculator.Calculator z
Exception in thread "main" java.util.EmptyStackException
	at java.util.Stack.peek(Stack.java:102)
	at java.util.Stack.pop(Stack.java:84)
	at ru.fizteh.fivt.students.dsalnikov.calculator.Calculator.main(Calculator.java:143)
```