program main
	implicit none
	character(100) S
	integer :: N, K
	read(*, *) N, K
	read(*, *) S
	if(S(K:K) == "A") then
		S(K:K) = "a"
	else if(S(K:K) == "B") then
		S(K:K) = "b"
	else
		S(K:K) = "c"
	end if
	write(*, *) trim(S)
end program main