Suppose portfolio ABC has a standard deviation of $23\%$ and an expected return of $11\%.$ The risk$-$free rate is $3\%.$ Consider an investor wishing to use ABC and the risk$-$free asset to achieve an expected return of $8\%.$ What will be the overall standard deviation this investor faces? Express your answer in decimal format, rounded accurately to $4$ decimal places $($e$.$g$.,10\mathrm{.}67\%$ should be expressed as $0\mathrm{.}1067$ and nothing else$).$