// EXPLOSION!
#define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
#include<unordered_set>
#include<unordered_map>
#include<chrono>
using namespace std;
typedef pair<int, int> pii;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pair<int, int>> vpi;
typedef vector<pair<ll, ll>> vpll;
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
#define pb push_back
#define mp make_pair
#define rsz resize
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define f first
#define s second
#define cont continue
#define endl '\n'
//#define ednl '\n'
#define test int testc;cin>>testc;while(testc--)
#define pr(a, b) trav(x,a)cerr << x << b; cerr << endl;
#define message cout << "Hello World" << endl;
const int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 }; // for every grid problem!!
const ll linf = 4000000000000000000LL;
const ll inf = 998244353;// 1000000007
void pv(vi a) { trav(x, a)cout << x << " "; cout << endl; }void pv(vll a) { trav(x, a)cout << x << " "; cout << endl; }void pv(vector<vi>a) {
F0R(i, sz(a)) { cout << i << endl; pv(a[i]); cout << endl; }
}void pv(vector<vll>a) { F0R(i, sz(a)) { cout << i << endl; pv(a[i]); }cout << endl; }void pv(vector<string>a) { trav(x, a)cout << x << endl; cout << endl; }
void setIO(string s) {
ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef arwaeystoamneg
if (sz(s))
{
freopen((s + ".in").c_str(), "r", stdin);
if (s != "test1")
freopen((s + ".out").c_str(), "w", stdout);
}
#endif
}
#ifndef arwaeystoamneg
#include<dna.h>
#endif
const int MAX = 111111;
int prefix[MAX][3], prefix1[MAX][3][3], temp[3][3];
int n;
map<char, int>key = { {'A',0},{'C',1},{'T',2} };
void init(std::string a, std::string b)
{
n = sz(a);
F0R(i, n)
{
F0R(j, 3)prefix[i + 1][j] = prefix[i][j];
prefix[i + 1][key[a[i]]]++;
prefix[i + 1][key[b[i]]]--;
F0R(j, 3)F0R(k, 3)prefix1[i + 1][j][k] = prefix1[i][j][k];
prefix1[i + 1][key[a[i]]][key[b[i]]]++;
}
}
int get_distance(int l, int r)
{
F0R(i, 3)if (prefix[r + 1][i] != prefix[l][i])return -1;
F0R(i, 3)F0R(j, 3)temp[i][j] = prefix1[r + 1][i][j] - prefix1[l][i][j];
int ans = 0;
F0R(i, 3)temp[i][i] = 0;
F0R(i, 3)
{
F0R(j, 3)
{
int x = min(temp[i][j], temp[j][i]);
ans += x;
temp[i][j] -= x;
temp[j][i] -= x;
}
}
ans += 2 * (*max_element(temp[0], temp[0] + 3));
return ans;
}
#ifdef arwaeystoamneg
int main()
{
setIO("test1");
int n, q;
assert(scanf("%d %d", &n, &q) == 2);
char A[MAX + 1], B[MAX + 1];
assert(scanf("%s", A) == 1);
assert(scanf("%s", B) == 1);
std::string a = std::string(A);
std::string b = std::string(B);
std::vector<int> x(q), y(q);
for (int i = 0; i < q; i++) {
assert(scanf("%d %d", &x[i], &y[i]) == 2);
}
fclose(stdin);
std::vector<int> results(q);
init(a, b);
for (int i = 0; i < q; i++) {
results[i] = get_distance(x[i], y[i]);
}
for (int i = 0; i < q; i++) {
printf("%d\n", results[i]);
}
fclose(stdout);
return 0;
}
#endif
