notBlocked =: {{
	first =. x={.y
	notThere =. -.x e. y
	first +. notThere
}}

nextChar =: {{
	*./;x notBlocked each y
}}"0 1

solve =: {{
	result =. ''
	data =. 'b' fread 'p079_keylog.txt'
	chars =. ~.;data
	while. 0<#chars do.
		ch =. {.chars{~I. chars nextChar data
		result =. result,ch
		removeCh =. ch&(~:#])
		chars =. removeCh chars
		data =. removeCh each data
	end.
	result
}}

problem79 =: solve ''