#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include <bits/stdc++.h>
using namespace std;

#define sim template < class c
#define ris return * this
#define mor > muu & operator << (
#define R22(r) sim > typename \
  enable_if<1 r sizeof dud<c>(0), muu&>::type operator<<( c g) {
sim > struct rge { c b, e; };
sim > rge<c> range(c h, c n) { return {h, n}; }
sim > auto dud(c * r) -> decltype(cerr << *r);
sim > char dud(...);
struct muu {
	#ifdef LOCAL
	stringstream a;
	~muu() { cerr << a.str() << endl; }
	R22(<) a << boolalpha << g; ris; }
	R22(==) ris << range(begin(g), end(g)); }
	sim, class b mor pair < b, c> r) { ris << "(" << r.first << ", " << r.second << ")"; }
	sim mor rge<c> u) {
		a << "[";
		for (c i = u.b; i != u.e; ++i) 
			*this << ", " + 2 * (i == u.b) << *i;
		ris << "]";
	}
#else
sim mor const c&) { ris; }
#endif
muu & operator()() { ris; }
};
#define imie(r...) "[" #r ": " << (r) << "] "
#define debug (muu() << __FUNCTION__ << "#" << __LINE__ << ": ")

int G[5][5];

vector<int> szukaj_cykl(int a, vector<int> cyc, int zos) {
	int x = cyc.back();
	if (G[x][a] > 0) return cyc;
	if (zos == 1) return vector<int>();
	for (int y  = 0; y < 4; y ++) {
		if (G[x][y] > 0) {
			cyc.push_back(y);
			auto r = szukaj_cykl(a, cyc, zos -1);
			if (!r.empty()) return r;
			cyc.pop_back();
		}
	}
	return vector<int>();
}

int main() {
	ios_base::sync_with_stdio(0);
	string a, b;
	cin >> a >> b;
	int n = a.size();
	map<char,int> mapa;
	mapa['G'] = 0;
	mapa['C'] = 1;
	mapa['A'] = 2;
	mapa['T'] = 3;
	for (int i = 0; i < n; i ++) {
		G[mapa[a[i]]][mapa[b[i]]] ++;
	}
	
	int res = 0;
	
	for (int k = 1; k <= 4; k ++) {
		for (int i = 0; i < 4; i ++) {
			while(1) {
			auto v = szukaj_cykl(i, {i}, k);
			if (v.empty()) break;
			int MIN = n;
			for (int i = 1; i < v.size(); i ++) {
				MIN = min(MIN, G[v[i-1]][v[i]]);
			}
			MIN = min(G[v.back()][v[0]], MIN);
			
			debug << v;
			debug << imie(MIN);
			
			res += MIN * (k-1);
			
			for (int i = 1; i < v.size(); i ++) {
				G[v[i-1]][v[i]]-= MIN;
			}
			G[v.back()][v[0]] -= MIN;
		}
	}
}
//~ for (int i = 0; i < 4; i ++) {
	//~ for (int j = 0; j < 4; j ++) {
		//~ debug << G[i][j] << " ";;
	//~ }
	//~ debug << "\n";
//~ }
cout << res;
}