#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i=0;i<(n);i++)


int get(char c)
{
    if(c=='A')
        return 0;
    if(c=='C')
        return 1;
    if(c=='G')
        return 2;
    if(c=='T')
        return 3;
}
int G[5][5];
vector <vector<int> > Q [5];
int n;
int ans=0;

void pre()
{
    string A,B;
    cin>>A>>B;
    n=A.size();
    rep(i,n)
        G[get(A[i])][get(B[i])]++;   
    for (int S=1;S<16;S++)
    {
        vector<int> SS;
        rep(i,4)
            if(S&(1<<i))
                SS.push_back(i);
        rep(i,30)
        {
            next_permutation(SS.begin(),SS.end());
            Q[SS.size()].push_back(SS);
        }
    }
}

void solve()
{
    for (int k=1;k<5;k++)
    {
        for (auto V:Q[k])
        {
            int m=1e9;
            rep(i,V.size())
                m=min(G[V[i]][V[(i+1)%V.size()]],m);
           rep(i,V.size())
                G[V[i]][V[(i+1)%V.size()]]-=m;
            ans+=m*(V.size()-1);
        }
    }
}


main()
{
    pre();
    solve();
    cout <<ans<<endl;
}