fun main (args : Array<String>) {
	val (len, num1) = readLine()!!.split(" ").map(String::toInt)
	val str1 = readLine()
	var num2 : Int = num1.toInt()
	var str2 : String = str1.toString()
	var count : Int = 0
	var result : String = ""
	for (i in str2) {
		count++
		if (count == num2) {
			if (i.toString() == "A") {
				result += "a"
			} else if (i.toString() == "B") {
				result += "b"
			} else if (i.toString() == "C") {
				result += "c"
			}
		} else {
			result += i
		}
	}
	println("${result}")
}