#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int pref[N], cnt[2][N][3];
char c[3] = {'A', 'C', 'T'};
int get_distance(int l, int r) {
++l, ++r;
for (int i = 0; i < 3; i++) {
if ((cnt[0][r][i] - cnt[0][l - 1][i]) != (cnt[1][r][i] - cnt[1][l - 1][i])) {
return -1;
}
}
return (pref[r] - pref[l - 1] + 1) / 2;
}
void init(string a, string b) {
int n = (int) a.size();
for (int i = 0; i < n; i++) {
pref[i + 1] = pref[i] + (a[i] != b[i] ? 1 : 0);
for (int j = 0; j < 3; j++) {
cnt[0][i + 1][j] += cnt[0][i][j];
cnt[1][i + 1][j] += cnt[1][i][j];
cnt[0][i + 1][j] += a[i] == c[j];
cnt[1][i + 1][j] += b[i] == c[j];
}
}
}
