petar's shitty game

package com.carDealer.controllers;

import java.util.Scanner;

public class t {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        //input
        long start = Integer.parseInt(sc.nextLine());
        long end = Integer.parseInt(sc.nextLine());
        String str = sc.nextLine();

        long sum = 0;
        for (long i = start; i < end; i++) {
            if (i % 5 == 0) {
                sum += i;
            } else {
                sum += (i % 5);
            }
        }

        String sumStr = String.valueOf(sum);
        if (sum % 2 == 0) {
            String charToReplace = String.valueOf(sumStr.charAt(0));
            System.out.printf("%s", sumStr.replaceAll(charToReplace, str));
        } else {
            String charToReplace = String.valueOf(sumStr.charAt(sumStr.length() - 1));
            System.out.printf("%s", sumStr.replaceAll(charToReplace, str));
        }
    }
}