#include <bits/stdc++.h>
#define pb push_back
#define eb emplace_back
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define uniq(x) x.erase(unique(all(x)), x.end())
#define rall(x) x.rbegin(), x.rend()
//#define int long long
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int mod = 1e9 + 7;
const int LOG = 20;
const int maxn = 1e5 + 5;
const double eps = 1e-9;
void setIO() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
string a, b;
int n;
bool sub3 = 1;
vector<vector<int> > prefixA, prefixT, prefixC;
vector<int> prefixAT, prefixAC, prefixCT;
void init(string x, string y) {
a = x;
b = y;
n = sz(a);
for(char &ch : a) sub3 = sub3 && (ch == 'C');
for(char &ch : b) sub3 = sub3 && (ch == 'C');
prefixA.resize(2, vector<int>(n+1, 0));
prefixT.resize(2, vector<int>(n+1, 0));
prefixC.resize(2, vector<int>(n+1, 0));
prefixAT.resize(n+1, 0);
prefixCT.resize(n+1, 0);
prefixAC.resize(n+1, 0);
for(int i=0; i<n; i++) {
prefixAT[i+1] = prefixAT[i] + (a[i] != b[i] && ((a[i] == 'A' && b[i] == 'T') || (a[i] == 'T' && b[i] == 'A')));
prefixCT[i+1] = prefixCT[i] + (a[i] != b[i] && ((a[i] == 'C' && b[i] == 'T') || (a[i] == 'T' && b[i] == 'C')));
prefixAC[i+1] = prefixAC[i] + (a[i] != b[i] && ((a[i] == 'A' && b[i] == 'C') || (a[i] == 'C' && b[i] == 'A')));
prefixA[0][i+1] = prefixA[0][i] + (a[i] == 'A');
prefixA[1][i+1] = prefixA[1][i] + (b[i] == 'A');
prefixT[0][i+1] = prefixT[0][i] + (a[i] == 'T');
prefixT[1][i+1] = prefixT[1][i] + (b[i] == 'T');
prefixC[0][i+1] = prefixC[0][i] + (a[i] == 'C');
prefixC[1][i+1] = prefixC[1][i] + (b[i] == 'C');
}
}
int get_distance(int x, int y) {
if(x == y) return (a[x] == b[x] ? 0 : -1);
if(y - x == 1) {
string s1 = "";
string s2 = "";
for(int i=x; i<=y; i++) s1 += a[i], s2 += b[i];
if(s1 == s2) return 0;
sort(all(s2));
sort(all(s1));
if(s1 != s2) return -1;
return 1;
}
if(y - x == 2) {
string s1 = "";
string s2 = "";
for(int i=x; i<=y; i++) s1 += a[i], s2 += b[i];
int ok = 0;
for(int i=0; i<sz(s1); i++) ok += (s1[i] == s2[i]);
sort(all(s1));
sort(all(s2));
if(s1 != s2) return -1;
if(ok == 3) return 0;
if(ok == 1) return 1;
if(ok == 0) return 2;
}
if(y - x <= 100000) {
if(prefixA[0][y+1] - prefixA[0][x] != prefixA[1][y+1] - prefixA[1][x]) return -1;
if(prefixT[0][y+1] - prefixT[0][x] != prefixT[1][y+1] - prefixT[1][x]) return -1;
if(prefixC[0][y+1] - prefixC[0][x] != prefixC[1][y+1] - prefixC[1][x]) return -1;
int d1 = (prefixAT[y+1] - prefixAT[x] + 1) / 2;
int d2 = (prefixCT[y+1] - prefixCT[x] + 1) / 2;
int d3 = (prefixAC[y+1] - prefixAC[x] + 1) / 2;
return d1 + d2 + d3;
}
return 0;
}
// int32_t main() {
// setIO();
// string x, y;
// cin >> x >> y;
// init(x, y);
// cout << get_distance(0, 0) << '\n';
// cout << get_distance(0, 1) << '\n';
// cout << get_distance(0, 2) << '\n';
// return 0;
// }
