#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<int> diff;
void init(string a, string b){
n = sz(a);
coua.resize(n);coub.resize(n);diff.resize(n);
for(int i = 0; i < n; i++){
if(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] == 'A' ? 0 : (a[i] == 'T' ? 1 : 2);
coua[i][xa]++;
int xb = b[i] == 'A' ? 0 : (b[i] == 'T' ? 1 : 2);
coub[i][xb]++;
}
for(int i = 0; i < n; i++){
if(i){
diff[i] = diff[i - 1];
}
if(a[i] != b[i])diff[i]++;
}
}
int get_distance(int x, int y){
if(!x){
if(coua[y][0] != coub[y][0] or coua[y][1] != coub[y][1] or coua[y][2] != coub[y][2])return -1;
}
else{
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;
}
}
if(!x){
return diff[y] / 2 + (diff[y] % 2);
}
else{
return (diff[y] - diff[x - 1]) / 2 + ((diff[y] - diff[x - 1]) % 2);
}
}
/*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;
}*/
