#include <bits/stdc++.h>
#define endline "\n"
#define pb push_back
#define mp make_pair
#define st first
#define nd second
#define lsb(i) i&(-i)
#define sz(i) (int)i.size()
typedef long long ll;
using namespace std;
const ll INF = 1e18L;
constexpr int mod = int(1e9) + 7;
ll t=1, n, q, k, cases = 0;
string a, b;
vector<array<int,3>> coua,coub; // 0 = A, 1 = T, 2 = C
vector<array<int,6>> diff; // 0 = TA, 1 = AT, 2 = CA, 3 = AC, 4 = TC, 5 = CT
void init(string a, string b){
n = sz(a);
coua.resize(n + 1);coub.resize(n + 1);diff.resize(n + 1);
for(int i = 1; i <= n; i++){
for(int j = 0; j < 3; j++){
coua[i][j] = coua[i - 1][j];
coub[i][j] = coub[i - 1][j];
}
int xa = a[i - 1] == 'A' ? 0 : (a[i - 1] == 'T' ? 1 : 2);
coua[i][xa]++;
int xb = b[i - 1] == 'A' ? 0 : (b[i - 1] == 'T' ? 1 : 2);
coub[i][xb]++;
}
for(int i = 1; i <= n; i++){
for(int j = 0; j < 6; j++){
diff[i][j] = diff[i - 1][j];
}
if(a[i - 1] == 'T'){
if(b[i - 1] == 'A')diff[i][0]++;
else if(b[i - 1] == 'C')diff[i][4]++;
}
else if(a[i - 1] == 'A'){
if(b[i - 1] == 'T')diff[i][1]++;
else if(b[i - 1] == 'C')diff[i][3]++;
}
else{
if(b[i - 1] == 'A')diff[i][2]++;
else if(b[i - 1] == 'T')diff[i][5]++;
}
}
}
int get_distance(int x, int y){
x++;y++;
if(coua[y][0] - coua[x - 1][0] != coub[y][0] - coub[x - 1][0]){
return -1;
}
else if(coua[y][1] - coua[x - 1][1] != coub[y][1] - coub[x - 1][1]){
return -1;
}
else if(coua[y][2] - coua[x - 1][2] != coub[y][2] - coub[x - 1][2]){
return -1;
}
ll ans = 0, bruh = 0;
ans += min(diff[y][0] - diff[x - 1][0], diff[y][1] - diff[x - 1][1]);
bruh += abs((diff[y][0] - diff[x - 1][0]) - (diff[y][1] - diff[x - 1][1]));
//cout << ans << '/';
ans += min(diff[y][2] - diff[x - 1][2], diff[y][3] - diff[x - 1][3]);
bruh += abs((diff[y][2] - diff[x - 1][2]) - (diff[y][3] - diff[x - 1][3]));
//cout << ans << '/';
ans += min(diff[y][4] - diff[x - 1][4], diff[y][5] - diff[x - 1][5]);
bruh += abs((diff[y][4] - diff[x - 1][4]) - (diff[y][5] - diff[x - 1][5]));
//cout << diff[y][4] << " " << diff[x - 1][4] << " " << diff[y][5] << " " << diff[x - 1][5] << endline;
ans += (bruh / 3) * 2;
return ans;
}
/*int main(){
#ifdef local
freopen("trie.gir","r",stdin);
freopen("trie.cik","w",stdout);
#endif
ios_base::sync_with_stdio(false);cin.tie(NULL);
//cin>>t;
//for(; cases <= t; cases++)solve();
cin >> n >> q;
cin >> a >> b;
init(a, b);
for(int i = 0; i < q; i++){
int x, y;
cin >> x >> y;
cout << get_distance(x, y) << endline;
}
return 0;
}*/
