#include "dna.h"
#ifdef NYAOWO
#include "grader.cpp"
#endif
#include <bits/stdc++.h>
#define For(i, a, b) for(int i = a; i <= b; i++)
#define Forr(i, a, b) for(int i = a; i >= b; i--)
#define F first
#define S second
#define sz(x) ((int)x.size())
#define all(x) x.begin(), x.end()
#define eb emplace_back
// #define int LL
using namespace std;
using i32 = int32_t;
using LL = long long;
using pii = pair<int, int>;
namespace {
const int MAXN = 100'000;
int n;
int pre[3][3][MAXN + 10];
int ca[3], cb[3];
int cnt[3][3];
int ch2int(char ch) {
if(ch == 'A') return 0;
if(ch == 'T') return 1;
if(ch == 'C') return 2;
assert(false);
return -1;
}
void _init(string a, string b) {
n = sz(a);
For(c1, 0, 2) For(c2, 0, 2) pre[c1][c2][0] = 0;
For(i, 1, n) {
For(c1, 0, 2) For(c2, 0, 2) pre[c1][c2][i] = pre[c1][c2][i - 1];
int cha = ch2int(a[i - 1]);
int chb = ch2int(b[i - 1]);
pre[cha][chb][i]++;
}
}
int _get_distance(int l, int r) {
memset(ca, 0, sizeof(ca));
memset(cb, 0, sizeof(cb));
For(c1, 0, 2) For(c2, 0, 2) {
cnt[c1][c2] = pre[c1][c2][r] - pre[c1][c2][l - 1];
ca[c1] += cnt[c1][c2];
cb[c2] += cnt[c1][c2];
}
For(c, 0, 2) if(ca[c] != cb[c]) return -1;
int ans = 0;
auto owo = [&](int a, int b) {
int k = min(cnt[a][b], cnt[b][a]);
cnt[a][b] -= k;
cnt[b][a] -= k;
ans += k;
};
owo(0, 1);
owo(0, 2);
owo(1, 2);
return ans + max(cnt[0][1], cnt[1][0]) * 2;
}
}
void init(string a, string b) {
::_init(a, b);
}
int get_distance(int x, int y) {
return ::_get_distance(x + 1, y + 1);
}
/*
6 3
ATACAT
ACTATA
1 3
4 5
3 5
2
1
-1
*/
