// AOJ 1568: String Conversion
// 2018.2.16 bal4u

#include <stdio.h>
#include <stdlib.h>

int a['z'+1], b['z'+1];
char buf[100005];

int cmp(int *a, int *b) { return *b - *a; }

int main() 
{
	int i, x, ans;
	char *p;

	fgets(buf, 10, stdin);
	fgets(p=buf, sizeof(buf), stdin);
	while (*p > ' ') a[*p++]++;
	fgets(p=buf, sizeof(buf), stdin);
	while (*p > ' ') b[*p++]++;
	qsort(a + 'a', 26, sizeof(int), cmp);
	qsort(b + 'a', 26, sizeof(int), cmp);
	
	ans = 0;
	for (i = 'a'; i <= 'z'; i++) {
		x = a[i] - b[i];
		if (x >= 0) ans += x; else ans -= x;
	}
	printf("%d\n", ans >> 1);
	return 0; 
}

