import java.util.*;

public class Yukicoder225{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int m = scan.nextInt();
		String s = scan.next();
		String t = scan.next();
		int kazu = 0;
		for(int i = 0;i < s.length();i++){
			if(s.charAt(i) != t.charAt(i) || i == s.length() - 1){
				if(i == s.length() - 1 && s.length() < m){
					s += t.substring(s.length() , s.length() + 1);
					if(s.length() == m){
						kazu++;
						break;
					}
				}else if(s.charAt(i + 1) == t.charAt(i)){
					s = s.substring(0,i) + s.substring(i+1,s.length());
				}else{
					s = s.substring(0,i) + t.substring(i,i+1) + s.substring(i+1,s.length());
				}
				kazu++;
			}
		}
		System.out.println(kazu);
	}
}