#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,popcnt,sse4,abm")
#include <bits/stdc++.h>
using namespace std;
#ifndef WAIMAI
#include "dna.h"
#endif
#ifdef WAIMAI
#define debug(HEHE...) cout << "[" << #HEHE << "] : ", dout(HEHE)
void dout() {cout << '\n';}
template<typename T, typename...U>
void dout(T t, U...u) {cout << t << (sizeof...(u) ? ", " : ""), dout(u...);}
#else
#define debug(...) 7122
#endif
#define ll long long
#define Waimai ios::sync_with_stdio(false), cin.tie(0)
#define FOR(x,a,b) for (int x = a, I = b; x <= I; x++)
#define pb emplace_back
#define F first
#define S second
const int SIZE = 1e5 + 5;
int n;
int prea[SIZE][3];
int preb[SIZE][3];
int pre2[SIZE][3][3];
void init(string a, string b) {
n = a.size();
a = " " + a;
b = " " + b;
FOR (i, 1, n) {
FOR (j, 0, 2) {
prea[i][j] = prea[i - 1][j];
preb[i][j] = preb[i - 1][j];
FOR (k, 0, 2) pre2[i][j][k] = pre2[i - 1][j][k];
}
int x = (a[i] == 'A' ? 0 : a[i] == 'T' ? 1 : 2);
int y = (b[i] == 'A' ? 0 : b[i] == 'T' ? 1 : 2);
prea[i][x]++;
preb[i][y]++;
pre2[i][x][y]++;
}
}
int cnt[3][3];
int get_distance(int l, int r) {
l++, r++;
FOR (i, 0, 2) if (prea[r][i] - prea[l - 1][i] != preb[r][i] - preb[l - 1][i]) return -1;
memset(cnt, 0, sizeof(cnt));
FOR (i, 0, 2) {
FOR (j, 0, 2) cnt[i][j] = pre2[r][i][j] - pre2[l - 1][i][j];
cnt[i][i] = 0;
}
int ans = 0, mx = 0;
FOR (i, 0, 2) FOR (j, i + 1, 2) {
int &x = cnt[i][j], &y = cnt[j][i];
int delta = min(x, y);
ans += delta;
x -= delta, y -= delta;
}
FOR (i, 0, 2) FOR (j, 0, 2) mx = max(mx, cnt[i][j]);
ans += 2 * mx;
return ans;
}
/*
in1
6 3
ATACAT
ACTATA
1 3
4 5
3 5
out1
2
1
-1
*/
#ifdef WAIMAI
int main() {
int n, q;
assert(scanf("%d %d", &n, &q) == 2);
char A[n+1], B[n+1];
assert(scanf("%s", A) == 1);
assert(scanf("%s", B) == 1);
string a = string(A);
string b = string(B);
vector<int> x(q), y(q);
for (int i = 0; i < q; i++) {
assert(scanf("%d %d", &x[i], &y[i]) == 2);
}
fclose(stdin);
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
