#include <bits/stdc++.h>
#define st first
#define nd second
#define fi first
#define se second
#define pb push_back
#define ps(v) cout << v << " "
#define pln(v) cout << v << "\n"
#define entr cout << "\n"

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> pll;


const ll MAX = 4;
const ll INF = 1e9;
ll g[MAX][MAX];
ll dis[MAX][MAX], last[MAX][MAX];

ll toNum(char c) {
	switch (c) {
		case 'A': return 0;
		case 'C': return 1;
		case 'G': return 2;
		case 'T': return 3;
	}
}

char toC(ll c) {
	switch (c) {
		case 0: return 'A';
		case 1: return 'C';
		case 2: return 'G';
		case 3: return 'T';
	}
}

void floyd() {
	
	for (int i = 0; i < MAX; ++i) {
		for (int j = 0; j < MAX; ++j) if (i != j && g[i][j] > 0) {
			dis[i][j] = 1;
		} else dis[i][j] = INF;
	}
	
	for (int k = 0; k < MAX; ++k) {
		for (int i = 0; i < MAX; ++i) {
			for (int j = 0; j < MAX; ++j) {
				if (dis[i][k] + dis[k][j] < dis[i][j]) { 
					dis[i][j] = dis[i][k] + dis[k][j];
				}
			}
		}
	}
	
}

int main() {
	ios_base::sync_with_stdio(0);
	string str1, str2;
	cin >> str1 >> str2;
	for (int i = 0; i < str1.size(); ++i) {
		ll a = toNum(str1[i]);
		ll b = toNum(str2[i]);
		g[a][b]++;
	}
	
	vector<ll> pom;
	ll result = 0;
	for (int mask = 1; mask < 16; ++mask) if (__builtin_popcount(mask) > 1){
		pom.clear();
		for (int i = 0; i < 4; ++i) if (mask & (1 << i)) {
			pom.pb(i);
		}
		
		do {
			ll cycles = g[pom[0]][pom[1]];
			for (int i = 0; i + 1 < pom.size(); ++i) {
				cycles = min(cycles, g[pom[i]][pom[i+1]]);
			}
			cycles = min(cycles, g[pom[pom.size()-1]][pom[0]]);
			
			for (int i = 0; i + 1 < pom.size(); ++i) {
				g[pom[i]][pom[i+1]] -= cycles;
			}
			g[pom[pom.size()-1]][pom[0]] -= cycles;
			
			result += cycles *(__builtin_popcount(mask) - 1);
			/*
			for (int i = 0; i < pom.size(); ++i) {
				cout << toC(pom[i]);
			}
			cout << endl;
			* */
			
		} while (next_permutation(pom.begin(), pom.end()));
	}
	
	cout << result;
	return 0;
}