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

public class Main {
    static char[] start;
    static char[] term;
    static int[][] dp;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int m = sc.nextInt();
        start = sc.next().toCharArray();
        term = 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 x, int y) {
        if (x < 0) {
            return y + 1;
        }
        if (y < 0) {
            return x + 1;
        }
        if (dp[x][y] < 0) {
            if (start[x] == term[y]) {
                dp[x][y] = dfw(x - 1, y - 1);
            } else {
                dp[x][y] = Math.min(dfw(x - 1, y - 1), Math.min(dfw(x - 1, y), dfw(x, y - 1))) + 1;
            }
        }
        return dp[x][y];
    }
}
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 {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}