/*
$$$$$$$\ $$\ $$$$$$$\
$$ __$$\ \__| $$ __$$\
$$ | $$ | $$$$$$\ $$$$$$\ $$\ $$$$$$$\ $$ | $$ | $$$$$$\ $$$$$$\ $$$$$$$\ $$$$$$\
$$$$$$$\ |$$ __$$\ $$ __$$\ $$ |$$ _____|$$$$$$$\ | \____$$\ $$ __$$\ $$ _____|\____$$\
$$ __$$\ $$ / $$ |$$ | \__|$$ |\$$$$$$\ $$ __$$\ $$$$$$$ |$$ | \__|$$ / $$$$$$$ |
$$ | $$ |$$ | $$ |$$ | $$ | \____$$\ $$ | $$ |$$ __$$ |$$ | $$ | $$ __$$ |
$$$$$$$ |\$$$$$$ |$$ | $$ |$$$$$$$ |$$$$$$$ |\$$$$$$$ |$$ | \$$$$$$$\\$$$$$$$ |
\_______/ \______/ \__| \__|\_______/ \_______/ \_______|\__| \_______|\_______|
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define PB push_back
#define MP make_pair
#define INS insert
#define LB lower_bound
#define UB upper_bound
#define pii pair <int,int>
#define pll pair <long long, long long>
#define X first
#define Y second
#define _ << " " <<
#define sz(x) (int)x.size()
#define all(a) (a).begin(),(a).end()
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORD(i, a, b) for (int i = (a); i > (b); --i)
#define FORA(i, x) for (auto &i : x)
#define REP(i, n) FOR(i, 0, n)
#define BITS(x) __builtin_popcount(x)
#define SQ(a) (a) * (a)
#define TRACE(x) cout << #x " = " << (x) << '\n';
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define umap unordered_map
typedef long long ll;
typedef long double ld;
typedef vector <int> vi;
typedef vector <pii> vpi;
typedef vector <ll> vll;
typedef vector <pll> vpl;
typedef vector <double> vd;
typedef vector <ld> vld;
typedef vector<string> vs;
typedef tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
//find_by_order -> kti najmanji
//order_of_key -> koliko ima manjih od x
//((float) t)/CLOCKS_PER_SEC
const int MOD = 1e9 + 7;
const double PI = acos(-1);
const int INF = 1e9 + 10;
const ll INFL = 1e18 + 10;
const int ABC = 30;
const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};
const int dox[] = {-1, 1, 0, 0, -1, -1, 1, 1};
const int doy[] = {0, 0, -1, 1, -1, 1, -1, 1};
inline int sum(int a, int b){
if (a + b < 0)
return (a + b + MOD) % MOD;
return (a + b) % MOD;
}
inline void add(int &a, int b){
a = sum(a, b);
}
inline int mul(ll a, ll b){
return ((a % MOD) * ((ll)b % MOD)) % MOD;
}
inline int sub(int a, int b){
return (a - b + MOD) % MOD;
}
inline int fast_pot(ll pot, ll n){
ll ret = 1;
while (n){
if (n & 1LL)
ret = (ret * pot) % MOD;
pot = (pot * pot) % MOD;
n >>= 1LL;
}
return ret;
}
inline int divide(int a, int b){
return mul(a, fast_pot(b, MOD - 2));
}
ll lcm(ll a, ll b){
return abs(a * b) / __gcd(a, b);
}
inline int ccw(pii a, pii b, pii c) {
return a.X * (b.Y - c.Y) + b.X * (c.Y - a.Y) + c.X * (a.Y - b.Y);
}
inline int CCW(pii A, pii B, pii C){
double val = ccw(A, B, C);
double eps = max(max(abs(A.X), abs(A.Y)), max(max(abs(B.X), abs(B.Y)), max(abs(C.X), abs(C.Y)))) / 1e9;
if (val <= -eps)
return -1;
if (val >= eps)
return 1;
return 0;
}
void to_upper(string &x){
REP(i, sz(x))
x[i] = toupper(x[i]);
}
void to_lower(string &x){
REP(i, sz(x))
x[i] = tolower(x[i]);
}
string its(ll x){
if (x == 0)
return "0";
string ret = "";
while (x > 0){
ret += (x % 10) + '0';
x /= 10;
}
reverse(all(ret));
return ret;
}
ll sti(string s){
ll ret = 0;
REP(i, sz(s)){
ret *= 10;
ret += (s[i] - '0');
}
return ret;
}
const int N = 1e5 + 10;
#include "dna.h"
string a, b;
int n, cnt[6][N], pref[2][ABC][N];
map <char, map <char, int>> w;
int getcnt(int i, int l, int r){
return cnt[i][r] - (l ? cnt[i][l - 1] : 0);
}
int getpref(int f, int i, int l, int r){
return pref[f][i][r] - (l ? pref[f][i][l - 1] : 0);
}
void init(string x, string y){
w['A']['T'] = 0;
w['A']['C'] = 1;
w['T']['A'] = 2;
w['T']['C'] = 3;
w['C']['A'] = 4;
w['C']['T'] = 5;
a = x;
b = y;
n = sz(a);
REP(i, n){
pref[0][a[i] - 'A'][i]++;
pref[1][b[i] - 'A'][i]++;
if (i){
REP(k, 2)
REP(j, ABC)
pref[k][j][i] += pref[k][j][i - 1];
}
}
REP(i, n){
if (a[i] != b[i])
cnt[w[a[i]][b[i]]][i]++;
if (i){
REP(j, 6){
cnt[j][i] += cnt[j][i - 1];
}
}
}
}
int get_distance(int l, int r){
//cout << getpref(0, 0, l, r) _ getpref(1, 0, l, r) _ getpref(0, 'T' - 'A', l, r) _ getpref(1, 'T' - 'A', l, r) _ getpref(0, 'C' - 'A', l, r) _ getpref(1, 'C' - 'A', l, r) << '\n';
if (getpref(0, 0, l, r) != getpref(1, 0, l, r) || getpref(0, 'T' - 'A', l, r) != getpref(1, 'T' - 'A', l, r) || getpref(0, 'C' - 'A', l, r) != getpref(1, 'C' - 'A', l, r))
return -1;
int c[6] = {0, 0, 0, 0, 0, 0};
REP(i, 6)
c[i] = getcnt(i, l, r);
int ret = 0;
//02 14 35
int x = min(c[0], c[2]);
c[0] -= x;
c[2] -= x;
ret += x;
x = min(c[1], c[4]);
c[1] -= x;
c[4] -= x;
ret += x;
x = min(c[3], c[5]);
c[3] -= x;
c[5] -= x;
ret += x;
//034 & 152
x = min({c[0], c[3], c[4]});
c[0] -= x;
c[3] -= x;
c[4] -= x;
ret += x * 2;
x = min({c[1], c[5], c[2]});
c[1] -= x;
c[2] -= x;
c[5] -= x;
ret += x * 2;
return ret;
}
void test(){
init("ATACAT", "ACTATA");
cout << get_distance(1, 3) << '\n';
cout << get_distance(4, 5) << '\n';
cout << get_distance(3, 5) << '\n';
}
