import java.util.*;
import java.io.*;
import static java.util.Arrays.*;
import static java.lang.Math.*;

public class No0225 {
    
    static final Scanner in = new Scanner(System.in);
    static final PrintWriter out = new PrintWriter(System.out,false);

    static void solve() {
        int n = in.nextInt();
        int m = in.nextInt();
        String s = in.next();
        String t = in.next();
        out.println(levenshteinDistance(s,t));
    }

    static int levenshteinDistance(String s, String t) {
    	int n = s.length();
    	int m = t.length();
    	int[][] dp = new int[n+1][m+1];
    	for (int i=0; i<=n; i++) {
    		for (int j=0; j<=m; j++) {
    			if (i == 0 && j == 0) continue;
    			dp[i][j] = Integer.MAX_VALUE/2;
    			if (i > 0) dp[i][j] = Math.min(dp[i][j], dp[i-1][j] + 1);
    			if (j > 0) dp[i][j] = Math.min(dp[i][j], dp[i][j-1] + 1);
    			if (i > 0 && j > 0) dp[i][j] = Math.min(dp[i][j], dp[i-1][j-1] + (s.charAt(i-1) == t.charAt(j-1) ? 0 : 1));
    		}
    	}
    	return dp[n][m];
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();

        solve();
        out.flush();

        long end = System.currentTimeMillis();
        //trace(end-start + "ms");
        in.close();
        out.close();
    }

    static void trace(Object... o) { System.out.println(Arrays.deepToString(o));}
}