#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int mxN=1e5;
map<char, int> mp;
int cnt1[mxN+1][3], cnt2[mxN+1][3][3], bad[mxN+1];
void init(string a, string b) {
mp['A']=0, mp['T']=1, mp['C']=2;
int n=a.size();
for (int i=0; i<n; ++i) {
for (int x=0; x<3; ++x) {
cnt1[i+1][x]=cnt1[i][x]+(mp[a[i]]==x)-(mp[b[i]]==x);
for (int y=0; y<3; ++y)
cnt2[i+1][x][y]=cnt2[i][x][y]+(mp[a[i]]==x&&mp[b[i]]==y);
}
bad[i+1]=bad[i]+(a[i]!=b[i]);
}
}
int get_distance(int x, int y) {
for (int i=0; i<3; ++i)
if (cnt1[y+1][i]-cnt1[x][i])
return -1;
int ans=0, extra=0;
for (int i=0; i<3; ++i)
for (int j=i+1; j<3; ++j) {
int a=cnt2[y+1][i][j]-cnt2[x][i][j];
int b=cnt2[y+1][j][i]-cnt2[x][j][i];
ans+=min(a, b);
extra+=max(a, b)-min(a, b);
}
assert(extra%3==0);
return ans+extra/3*2;
}
/*int main() {
ios::sync_with_stdio(0);
cin.tie(0);
init("ATACAT", "ACTATA");
cout << get_distance(1, 3) << " " << get_distance(4, 5) << " " << get_distance(3, 5);
return 0;
}*/
