Задача 1: Реализуйте поддержку унарного минуса

<Digit> ::= [0-9]
<UnsignedInteger> ::= "0" | ( [1-9] <Digit>* )
<Integer> ::= "-" <UnsignedInteger> | <UnsignedInteger>
<Multiplier> ::= "-" <Multiplier> | <Integer>
<Multiplication> ::= <Multiplier> "*" <Multiplier>
<Division> ::= <Multiplier> "/" <Multiplier>
<Term> ::= <Multiplier> ( "*" <Multiplier> | "/" <Multiplier> )*
<Addition> ::= <Term> "+" <Term>
<Subtraction> ::= <Term> "-" <Term>
<Expression> ::= <Term> ( "+" <Term> | "-" <Term> )*