import java.util.*;
import java.math.*;

public class Main {
    static HashMap<String, HashMap<String, Integer>> all = new HashMap<>();
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        System.out.println(getCount(sc.next(), sc.next()));
    }
    
    static int getCount(String aSb, String bSb) {
        HashMap<String, Integer> tmp = all.get(aSb);
        if (tmp != null && tmp.containsKey(bSb)) {
            return tmp.get(bSb);
        }
        int min = Integer.MAX_VALUE;
        if (aSb.length() == 0 || bSb.length() == 0) {
            return aSb.length() + bSb.length();
        }
        String aaSb = aSb.substring(1, aSb.length());
        String bbSb = bSb.substring(1, bSb.length());
        if (aSb.charAt(0) == bSb.charAt(0)) {
            min = getCount(aaSb, bbSb);
        } else {
            min = Math.min(min, getCount(aSb, bbSb) + 1);
            min = Math.min(min, getCount(aaSb, bSb) + 1);
            min = Math.min(min, getCount(aaSb, bbSb) + 1);
        }
        if (tmp == null) {
            tmp = new HashMap<String, Integer>();
            all.put(aSb, tmp);
        }
        tmp.put(bSb, min);
        return min;
    }
}