func main()
	var s: char :: cui@inputChar()
	var e: char :: cui@inputChar()
	var n: int :: cui@inputInt()
	if(n < 2 & s <> e)
		do cui@print("-1\n")
	else
		do cui@print("\{s}\{[e].repeat(n - 1)}\n")
	end if
end func