function Main(input) {
  input = input.trim()
  input = input.split("\n");
  var N = input[1].split("");
  var A = input[0].split(" ").map(Number);
  N[A[1]-1] = hoge(N[A[1]-1]);
  
  console.log(N.join(""))

}Main(require("fs").readFileSync("/dev/stdin", "utf8"));
function hoge(N){
switch(N){
  case "A":
  return "a";
  break;
    case "B":
  return "b";
  break;
    case "C":
  return "c";
  break;
}
}