#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define fi first
#define se second
typedef long double ld;
const ld eps = 1e-8;
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
const ll inf = 1e18;
const ll mod = 1e9 + 7;
#include "dna.h"
string a, b;
vector<int> at, ta, ac, ca, ct, tc;
void init(string na, string nb) {
a = na;
b = nb;
int n = a.size();
at.resize(n + 1);
ta.resize(n + 1);
ac.resize(n + 1);
ca.resize(n + 1);
ct.resize(n + 1);
tc.resize(n + 1);
for (int i = 0; i < n; i++) {
ca[i + 1] = ca[i];
ac[i + 1] = ac[i];
at[i + 1] = at[i];
ta[i + 1] = ta[i];
ct[i + 1] = ct[i];
tc[i + 1] = tc[i];
if (a[i] == 'A' && b[i] == 'C') {
ac[i + 1]++;
}
if (a[i] == 'C' && b[i] == 'A') {
ca[i + 1]++;
}
if (a[i] == 'A' && b[i] == 'T') {
at[i + 1]++;
}
if (a[i] == 'T' && b[i] == 'A') {
ta[i + 1]++;
}
if (a[i] == 'C' && b[i] == 'T') {
ct[i + 1]++;
}
if (a[i] == 'T' && b[i] == 'C') {
tc[i + 1]++;
}
}
}
int get_distance(int x, int y) {
int AC = ac[y + 1] - ac[x],
CA = ca[y + 1] - ca[x],
AT = at[y + 1] - at[x],
TA = ta[y + 1] - ta[x],
CT = ct[y + 1] - ct[x],
TC = tc[y + 1] - tc[x];
if (AT + AC != CA + TA)
return -1;
if (TA + TC != AT + CT)
return -1;
if (CA + CT != AC + TC)
return -1;
return min(CA, AC) + min(CT, TC) + min(AT, TA) + 2 * (max(CA, AC) - min(AC, CA));
}
/*
int main() {
int n, q;
cin >> n >> q;
string na, nb;
cin >> na >> nb;
init(na, nb);
for (int qw = 0; qw < q; qw++) {
int x, y;
cin >> x >> y;
cout << get_distance(x, y) << '\n';
}
}
*/
