A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes: 't' that evaluates to true. 'f' that evaluates to false. '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr. '&(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical AND of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1. '|(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical OR of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1. Given a string expression that represents a boolean expression, return the evaluation of that expression. It is guaranteed that the given expression is valid and follows the given rules.