暴力解法

import java.util.*;

public class Main{
    public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        String c = sc.nextLine();
        String big = c.toUpperCase();
        String small = c.toLowerCase();
        int count = 0;
        for(char a : str.toCharArray()){
            if(String.valueOf(a).equals(big) || String.valueOf(a).equals(small)){
                count ++;
            }
        }
        System.out.println(count);
    }
}