Let L= {w | w cannot be written as st#ts with s, t EPSILON {a,b}*}. Show that L is not regular

Let L = {w w cannot be written as st#ts with s, t e {a,b}* }. Show that Lis not regular. Let L = {w w cannot be written as st#ts with s, t e {a,b}* }. Show that Lis not regular