题目

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		sc.nextLine();
		char[] sq1 = sc.next().toCharArray();
		sc.nextLine();
		char[] sq2 = sc.next().toCharArray();
		
		Map<Character,Integer> map = new HashMap<>();
		map.put('A', 0);
		map.put('C', 1);
		map.put('G', 2);
		map.put('T', 3);
		
		int res = 0;
		for(int i=0;i<n;i++) {
			if(map.get(sq1[i])+map.get(sq2[i])!=3) {
				for(int j=i+1;j<n;j++) {
					if((map.get(sq1[i])+map.get(sq2[j]) == 3)
							&&
						(map.get(sq1[j])+map.get(sq2[i]) == 3)) {
						char c =sq2[i];
						sq2[i] = sq2[j];
						sq2[j] = c;
					}	
				}
				res++;
			}
		}
		System.out.println(res);
				
		sc.close();
	}
}

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		sc.nextLine();
		char[] s1 = sc.next().toCharArray();
		sc.nextLine();
		char[] s2 = sc.next().toCharArray();
		
		Map<Character,Integer> map = new HashMap<>();
		map.put('A', 0);
		map.put('C', 1);
		map.put('G', 2);
		map.put('T', 3);
		int res = 0;
		for(int i=0;i<n;i++) {
			if(map.get(s1[i])+map.get(s2[i]) != 3) {
				for(int j=i+1;j<n;j++) {
					if(map.get(s1[i])+map.get(s2[j]) == 3
							&&
					   map.get(s2[i])+map.get(s1[j]) == 3
					  ) {
						char t = s2[i];
						s2[i] =s2[j];
						s2[j] = t;
            break;
					}
				}
            res++;
			}
		}
		System.out.println(res);
		
		
		sc.close();
	}
}