#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;
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');
}
int get_distance(int x, int y) {
if(sub3) {
vector<int> A(2, 0), T(2, 0);
int bad = 0;
for(int i=x; i<=y; i++) {
if(a[i] == 'A') A[0]++;
else if(a[i] == 'T') T[0]++;
if(b[i] == 'A') A[1]++;
else if(b[i] == 'T') T[1]++;
if(a[i] != b[i]) bad++;
}
if(A[0] != A[1] || T[0] != T[1]) return -1;
return (bad + 1) / 2;
}
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;
// }
