#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int pref[N][5][5], cnt[N][5][5];
void init(string s, string t){
int n = s.size();
s = '.' + s;
t = '.' + t;
vector<int> a(n + 1), b(n + 1);
for(int i = 1; i <= n; i++){
if(s[i] == 'A'){
a[i] = 1;
}
else if(s[i] == 'C'){
a[i] = 2;
}else a[i] = 3;
if(t[i] == 'A'){
b[i] = 1;
}
else if(t[i] == 'C'){
b[i] = 2;
}else b[i] = 3;
}
for(int i = 1; i <= n; i++){
for(int j = 1; j <= 3; j++){
for(int k = 1; k <= 3; k++){
pref[i][j][k] = pref[i - 1][j][k];
cnt[i][j][k] = cnt[i - 1][j][k];
}
}
cnt[i][a[i]][1]++;
cnt[i][b[i]][2]++;
pref[i][a[i]][b[i]]++;
}
}
int get_distance(int l, int r){
l++;r++;
for(int i = 1; i <= 3; i++){
int a = cnt[r][i][1] - cnt[l - 1][i][1];
int b = cnt[r][i][2] - cnt[l - 1][i][2];
if(a != b) return -1;
}
int ans = 0;
map< pair<int, int>, int> mp;
for(int i = 1; i <= 3; i++){
for(int j = 1; j <= 3; j++){
int a = pref[r][i][j] - pref[l - 1][i][j];
mp[{i, j}] = a;
}
}
for(int i = 1; i <= 3; i++){
for(int j = i + 1; j <= 3; j++){
int mn = min(mp[{i, j}], mp[{j, i}]);
ans += mn;
mp[{i, j}] -= mn;
mp[{j, i}] -= mn;
}
}
int cnt = 0;
for(int i = 1; i <= 3; i++){
for(int j = 1; j <= 3; j++){
if(i == j) continue;
cnt += mp[{i, j}];
}
}
ans += (2 * cnt) / 3;
return ans;
}
