import java.io.*;
import java.util.*;

public class Main {
    static char[] s;
    static char[] t;
    static int[][] dp;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int m = sc.nextInt();
        s = sc.next().toCharArray();
        t = sc.next().toCharArray();
        dp = new int[n][m];
        for (int[] arr : dp) {
            Arrays.fill(arr, -1);
        }
        System.out.println(dfw(n - 1, m - 1));
    }
    
    static int dfw(int a, int b) {
        if (a < 0) {
            return b + 1;
        }
        if (b < 0) {
            return a + 1;
        }
        if (dp[a][b] < 0) {
            if (s[a] == t[b]) {
                dp[a][b] = dfw(a - 1, b - 1);
            } else {
                dp[a][b] = Math.min(dfw(a - 1, b), Math.min(dfw(a, b - 1), dfw(a - 1, b - 1))) + 1;
            }
        }
        return dp[a][b];
    }
}

class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}