import itertools s1 = input() s2 = input() n = len(s1) dns = "ACGT"; m = {str(i)+str(j) : 0 for i in dns for j in dns} for i in range(n): if s1[i] != s2[i]: m[s1[i]+s2[i]] += 1 #print(m) ans = 0 for i in range(4): for j in range(i+1, 4): prs = min(m[dns[i]+dns[j]], m[dns[j]+dns[i]]) ans += prs m[dns[i]+dns[j]] -= prs m[dns[j]+dns[i]] -= prs #print(ans, m) for ss in itertools.permutations(dns, 3): s = ''.join(ss) #print(s) hrmas = min(m[s[0:2]], m[s[1:3]], m[s[2]+s[0]]) #if hrmas > 0: # print(s, hrmas) ans += 2*hrmas m[s[0:2]] -= hrmas m[s[1:3]] -= hrmas m[s[2]+s[0]] -= hrmas #print(ans, m) ans += 3 * max(m.values()) print(ans)