#include "bits/stdc++.h"
#ifndef LOCAL
#include "dna.h"
#endif // LOCAL
using namespace std;
int code(char c){
if(c == 'A') return 0;
if(c == 'T') return 1;
if(c == 'C') return 2;
return -1;
}
const int MAX = 1e5 + 5;
int n, pref[MAX][3][3];
void init(std::string a, std::string b) {
n = (int)a.size();
for(int i = 0; i < n; ++i){
for(int j = 0; j < 3; ++j){
for(int k = 0; k < 3; ++k){
pref[i + 1][j][k] = pref[i][j][k];
}
}
++pref[i + 1][code(a[i])][code(b[i])];
}
}
int A[3], B[3], cnt[3][3];
int get_distance(int x, int y) {
++x; ++y;
for(int i = 0; i < 3; ++i) {
A[i] = B[i] = 0;
for(int j = 0; j < 3; ++j){
cnt[i][j] = 0;
}
}
for(int i = 0; i < 3; ++i){
for(int j = 0; j < 3; ++j){
A[i] += pref[y][i][j] - pref[x - 1][i][j];
B[j] += pref[y][i][j] - pref[x - 1][i][j];
cnt[i][j] += pref[y][i][j] - pref[x - 1][i][j];
}
}
for(int i = 0; i < 3; ++i){
if(A[i] != B[i]){
return -1;
}
}
int ans = 0;
auto work_greedy = [&](int i, int j){
int x = min(cnt[i][j], cnt[j][i]);
ans += x;
cnt[i][j] -= x;
cnt[j][i] -= x;
};
for(int i = 0; i < 3; ++i){
for(int j = 0; j < 3; ++j){
work_greedy(i, j);
}
}
int rest = 0;
for(int i = 0; i < 3; ++i){
for(int j = 0; j < 3; ++j){
rest = max(rest, cnt[i][j]);
}
}
ans += rest * 2;
return ans;
}
#ifdef LOCAL
int main(){
init("ATACAT", "ACTATA");
cout << get_distance(1, 3) << '\n';
cout << get_distance(4, 5) << '\n';
cout << get_distance(3, 5) << '\n';
}
#endif // LOCAL
