import java.util.Scanner;


public class Main_yukicoder225 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int m = sc.nextInt();
        char[] s = sc.next().toCharArray();
        char[] t = sc.next().toCharArray();

        int[][] dp = new int[m + 1][n + 1];
        for (int i = 0; i <= m; i++) {
            for (int j = 0; j <= n; j++) {
            	if (i == 0 && j == 0) {
            		continue;
            	}
            	if (i == 0) {
            		dp[i][j] = dp[i][j - 1] + 1;
            	} else if (j == 0) {
            		dp[i][j] = dp[i - 1][j] + 1;
            	} else {
            		if (s[j - 1] == t[i - 1]) {
            			dp[i][j] = dp[i - 1][j - 1];
            		} else {
            			dp[i][j] = dp[i - 1][j - 1] + 1;
            		}
            		dp[i][j] = Math.min(dp[i][j], dp[i][j - 1] + 1);
            		dp[i][j] = Math.min(dp[i][j], dp[i - 1][j] + 1);
            	}
        	}
        }
        
        System.out.println(dp[m][n]);
        
        sc.close();
    }
}