import java.util.Scanner;

public class NickyEnMark {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		char[] s1 = scanner.next().toCharArray();
		char[] s2 = scanner.next().toCharArray();
		int a = 0;
		for (int i = 0; i < n; i++) {
			int c1 = (s1[i] + 26 - s2[i]) % 26;
			int c2 = (s2[i] + 26 - s1[i]) % 26;
			a += Math.min(c1, c2);
		}

		System.out.println(a);
	}
}