#include <iostream>
#include <cstring>
using namespace std;
int n;
string s1, s2;
int cnt[100005][3][3];
int id(char c) {
if (c == 'A') return 0;
else if (c == 'T') return 1;
else return 2;
}
void beautifyData() {
for (int i = 0; i < n; i++) {
cnt[i][id(s1[i])][id(s2[i])] = 1;
if (i > 0) {
for (int j = 0; j < 3; j++) {
for (int k = 0; k < 3; k++) {
cnt[i][j][k] += cnt[i - 1][j][k];
}
}
}
}
}
void init(string a, string b) {
s1 = a, s2 = b;
n = a.size();
beautifyData();
}
int get_distance(int x, int y) {
int mat[3][3];
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
mat[i][j] = cnt[y][i][j] - (x > 0 ? cnt[x - 1][i][j] : 0);
}
}
for (int i = 0; i < 3; i++) {
if (mat[i][0] + mat[i][1] + mat[i][2] != mat[0][i] + mat[1][i] + mat[2][i]) return -1;
}
int ans = 0;
for (int i = 0; i < 2; i++) {
for (int j = i + 1; j < 3; j++) {
int moves = min(mat[i][j], mat[j][i]);
ans += moves;
mat[i][j] -= moves;
mat[j][i] -= moves;
mat[i][i] += moves;
mat[j][j] += moves;
}
}
ans += mat[0][1];
mat[2][1] += mat[0][1];
mat[0][1] = 0;
ans += mat[0][2];
mat[1][2] += mat[0][2];
mat[0][2] -= 0;
ans += mat[2][1];
mat[2][1] = mat[1][2] = 0;
return ans;
}
