Replace all pie | Test Cases Are Not Passing

All the test cases are not passing. Not able to make out which test cases are failing.

import java.util.Scanner;

public class Main {

public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String input = sc.nextLine();
    System.out.println(replaceAllPie(input,0, false));
}

static String replaceAllPie(String input, int selectedIndex, boolean isPiPresent){

    String s = String.format("Input String=%s ,Length=%d, selectedIndex=%d, isPiPresent=%s",input,input.length(),selectedIndex,isPiPresent);
    //System.out.println(s);

    if(input.length() < selectedIndex + 2 && !isPiPresent) {
        //System.out.println("input.length() < selectedIndex + 2 && !isPiPresent");
        return "";
        //return "EMPTY";
    }


    if(input.length() < selectedIndex + 2 && isPiPresent) {
        //System.out.println("input.length() < selectedIndex + 2 && isPiPresent");
        return input;
    }

    String currentString = input.substring(selectedIndex,selectedIndex+2);

    if(currentString.equalsIgnoreCase("pi")){
        input = replacePiWithDecimal(input,selectedIndex);
        isPiPresent = true;
    }

    return replaceAllPie(input,selectedIndex+1, isPiPresent);

}


static String replacePiWithDecimal(String input, int selectedIndex){

    String pi = input.substring(selectedIndex,selectedIndex+2);
    String result;

    if("pi".equalsIgnoreCase(pi)){
        StringBuffer newInput = new StringBuffer();
        String fp = input.substring(0,selectedIndex);
        String piString = input.substring(selectedIndex,selectedIndex+2);
        String sp = input.substring(selectedIndex+2);
        String pieNumerical = "3.14";

        newInput.append(fp);
        newInput.append(pieNumerical);
        newInput.append(sp);

        result = newInput.toString();
    }
    else {
        result = input;
    }

    String s = String.format("replacePiWithDecimal Input String =%s ,OutputString %s",input,result);
    //System.out.println(s);
    return result;
}

}

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