#include <stdio.h>

#define FOR(i, n) for (int i=0; i<n; i++)

void run(void) {
	int n;
	char a[17], b[17];
	scanf("%d %s %s", &n, a, b);
	FOR(i, n)
		a[i] -= 'a', b[i] -= 'a';
	
	int res = 26;
	FOR(i, 1 << (n - 1)){
		int mask = i;
		int ma = 0, mb = 0; // character masks
		for (int j=0; j<n; j++, mask /= 2)
			if (mask % 2) // swap j-th character
				ma |= (1 << b[j]), mb |= (1 << a[j]);
			else
				mb |= (1 << b[j]), ma |= (1 << a[j]);
		
		int cnta = 0, cntb = 0;
		for (; ma | mb; ma /= 2, mb /= 2)
			cnta += ma % 2, cntb += mb % 2;
		
		cnta = (cnta > cntb) ? cnta : cntb;
		res = (res < cnta) ? res : cnta;
	}
	
	printf("%d\n", res);
}
int main(void) {
	int t;
	scanf("%d", &t);
	while (t--)
		run();
	return 0;
}