#include <bits/stdc++.h>
#include "dna.h"
#define Flag false
// include <ext/pb_ds/assoc_container.hpp>
// include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
using namespace std;
#define all(x) x.begin(), x.end()
#define pb push_back
// define ordered_set tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>
#define mpr make_pair
#define ln '\n'
void IO(string name){freopen((name+".in").c_str(),"r",stdin); freopen((name+".out").c_str(),"w",stdout);}
//#define int long long
string l, r;
vector <array<array<int,3>,3>> pref;
map <char,int> id;
int n;
void init(string a, string b) {
l = a, r = b;
n = (int)a.size();
pref.resize(n);
id['A'] = 0, id['T'] = 1, id['C'] = 2;
for ( int i = 0; i < n; i++ ){
for ( int j = 0; j < 3; j++ ){
for ( int k = 0; k < 3; k++ ){
if ( i ) pref[i][j][k] = pref[i-1][j][k];
}
}
pref[i][id[l[i]]][id[r[i]]]++;
}
}
int get(int l, int r, int x, int y){
int val = pref[r][x][y];
if ( l ) val -= pref[l-1][x][y];
return val;
}
int get_distance(int x, int y){
array <array<int,3>,3> p;
for ( int i = 0; i < 3; i++ ){
for ( int j = 0; j < 3; j++ ){
p[i][j] = get(x, y, i, j);
}
}
auto f = [&](int &a, int &b){
int Mn = min(a, b);
a -= Mn, b -= Mn;
return Mn;
};
int cnt = 0;
for ( int i = 0; i < 3; i++ ){
for ( int j = i+1; j < 3; j++ ){
cnt += f(p[i][j], p[j][i]);
}
}
if ( p[0][1] > p[1][2] ) return -1;
p[0][2] += p[0][1]; p[1][2] -= p[0][1];
cnt += p[0][1]; p[0][1] = 0;
if ( p[1][0] > p[2][1] ) return -1;
p[2][0] += p[1][0]; p[2][1] -= p[1][0];
cnt += p[1][0]; p[1][0] = 0;
for ( int i = 0; i < 3; i++ ){
for ( int j = i+1; j < 3; j++ ){
if ( p[i][j] != p[j][i] ) return -1;
cnt += p[i][j];
}
}
return cnt;
}
#if Flag
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int _n, q; cin >> _n >> q;
string a, b; cin >> a >> b;
init(a, b);
while ( q-- ){
int x, y; cin >> x >> y;
cout << get_distance(x, y) << ln;
}
cout << '\n';
/*
6 3
ATACAT ACTATA
1 3
4 5
3 5
answer: {2, 1, -1}
*/
}
#endif
