#include "bits/stdc++.h"
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...)
#endif
using ll = long long;
using pii = pair<int, int>;
#define F first
#define S second
#define sz(x) (int)((x).size())
#define all(x) (x).begin(), (x).end()
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll get_rand(ll l, ll r) {
assert(l <= r);
return uniform_int_distribution<ll> (l, r)(rng);
}
const int N = 1e5 + 3;
string c = "ATC";
vector<pair<char, char>> diff = {{'A', 'T'}, {'T', 'A'}, {'T', 'C'}, {'C', 'T'}, {'C', 'A'}, {'A', 'C'}};
int n;
int cnts[3][N], cntt[3][N];
int pdiff[6][N];
int get(int l, int r, int *p){
return p[r] - p[l - 1];
}
void init(string s, string t){
n = sz(s);
s = ' ' + s, t = ' ' + t;
for(int i = 1; i <= n; ++i){
for(int j = 0; j < 3; ++j){
cnts[j][i] = cnts[j][i - 1] + (s[i] == c[j]);
cntt[j][i] = cntt[j][i - 1] + (t[i] == c[j]);
}
pair<char, char> p = {s[i], t[i]};
for(int j = 0; j < 6; ++j)
pdiff[j][i] = pdiff[j][i - 1] + (diff[j] == p);
}
}
int get_distance(int x, int y){
++x, ++y;
for(int j = 0; j < 3; ++j)
if(get(x, y, cnts[j]) != get(x, y, cntt[j]))
return -1;
vector<int> cnt(6, 0);
for(int j = 0; j < 6; ++j)
cnt[j] = get(x, y, pdiff[j]);
int res = 0, rem = 0;
for(int j = 0; j < 6; j += 2){
int mn = min(cnt[j], cnt[j + 1]);
res += mn;
cnt[j] -= mn, cnt[j + 1] -= mn;
rem += cnt[j] + cnt[j + 1];
}
res += rem / 3 * 2;
return res;
}
// void solve(){
// cin >> n >> q;
// cin >> s >> t;
// init();
// while(q--){
// int x, y;
// cin >> x >> y;
// cout << get_distance(x, y);
// }
// }
// int32_t main() {
// cin.tie(nullptr)->sync_with_stdio(0);
// #define task "troll"
// if(fopen(task".inp", "r")){
// freopen(task".inp", "r", stdin);
// freopen(task".out", "w", stdout);
// }
// int test = 1;
// // cin >> test;
// for(int i = 1; i <= test; ++i){
// // cout << "Case #" << i << ": ";
// solve();
// }
// #ifdef LOCAL
// cerr << "\n[Time]: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
// #endif
// return 0;
// }
