#include <bits/stdc++.h>
using namespace std;
vector<unordered_map<char, unordered_map<char, int>>> counts {};
vector<unordered_map<char, int>> absolute_counts {};
void init(string a, string b)
{
const int n = a.size();
counts.resize(n + 1);
for (int i = 0; i < n; i++) {
counts[i + 1] = counts[i];
counts[i + 1][a[i]][b[i]]++;
}
}
int get_distance(int x, int y)
{
y++;
int ans {};
auto cnts = counts[y];
int doubles {};
for (auto a : { 'A', 'C', 'T' })
for (auto b : { 'A', 'C', 'T' })
cnts[a][b] -= counts[x][a][b];
unordered_map<char, int> counts_a {}, counts_b {};
for (auto a : { 'A', 'C', 'T' }) {
for (auto b : { 'A', 'C', 'T' }) {
counts_a[a] += cnts[a][b];
counts_b[b] += cnts[a][b];
}
}
for (auto a : { 'A', 'C', 'T' }) {
if (counts_a[a] != counts_b[a])
return -1;
}
for (auto a : { 'A', 'C', 'T' }) {
for (auto b : { 'A', 'C', 'T' }) {
if (b == a)
continue;
int take = min(cnts[a][b], cnts[b][a]);
doubles += take;
}
}
int triples {};
for (auto a : { 'A', 'C', 'T' }) {
for (auto b : { 'A', 'C', 'T' }) {
if (b == a)
continue;
for (auto c : { 'A', 'C', 'T' }) {
if (c == b || c == a)
continue;
auto cnts_ab = cnts[a][b];
auto cnts_bc = cnts[b][c];
auto cnts_ca = cnts[c][a];
int take = min({ cnts[a][b], cnts[b][c], cnts[c][a] });
triples += take;
}
}
}
return (triples * 2) / 3 + doubles / 2;
}
// auto main() -> int
// {
// init("ATACAT", "ACTATA");
// cout << get_distance(1, 3) << endl;
// cout << get_distance(4, 5) << endl;
// cout << get_distance(3, 5) << endl;
// }
