import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		String S = sc.next();
		String T = sc.next();
		S+="-";
		T+="-";
		int dp[][]=new int[1010][1010];
		for(int i=0;i<1010;i++) Arrays.fill(dp[i], 114514);
		dp[0][0]=0;
		for(int i=0;i<=n;i++){
			for(int j=0;j<=m;j++){
				if( S.charAt(i)==T.charAt(j)){
					dp[i+1][j+1]=Math.min(dp[i+1][j+1], dp[i][j]);
				}else{
					dp[i+1][j+1]=Math.min(dp[i+1][j+1], dp[i][j]+1);
				}
				dp[i+1][j]=Math.min(dp[i+1][j], dp[i][j]+1);
				dp[i][j+1]=Math.min(dp[i][j+1], dp[i][j]+1);

			}
		}
		System.out.println(dp[n][m]);

	}
}