object Main {
    def main(args: Array[String]): Unit = {
      val lines = io.Source.stdin.getLines().toSeq
      println(solve(lines))
    }

    def solve(lines: Seq[String]): String = {
      val Array(n, k) = lines.head.split(" ").map(_.toInt)
      val s = lines.tail.head.split("").filter(_.length > 0).take(n)
      debug(n, k, s)

      val str = s.map(v => v).toArray
      str(k - 1) = str(k - 1).toLowerCase()
      str.mkString("")
    }

    private def debug(x: Any): Unit = {
      if (System.getenv("LOCAL_DEBUG") != null) println(x)
    }
  }