#include "dna.h"
#include <bits/stdc++.h>
using namespace std;
const int mxN = 100005;
int pref[mxN], prefa1[mxN], prefc1[mxN], prefa2[mxN], prefc2[mxN];
void init(string a, string b) {
int n = int(a.length());
for(int i = 0; i < n; i++) {
pref[i+1] = pref[i], prefa1[i+1] = prefa1[i], prefc1[i+1] = prefc1[i], prefa2[i+1] = prefa2[i], prefc2[i+1] = prefc2[i];
if(a[i] != b[i])
pref[i+1]++;
if(a[i] == 'A')
prefa1[i+1]++;
if(a[i] == 'C')
prefc1[i+1]++;
if(b[i] == 'A')
prefa2[i+1]++;
if(b[i] == 'C')
prefc2[i+1]++;
}
}
int ceil(int a, int b) {
return a%b == 0 ? a/b : a/b+1;
}
int get_distance(int x, int y) {
y++;
if(prefa2[y]-prefa2[x] != prefa1[y]-prefa1[x] || prefc2[y]-prefc2[x] != prefc1[y]-prefc2[x])
return -1;
return ceil(pref[y]-pref[x], 2);
}
/*
int main() {
string a, b;
cin >> a >> b;
init(a, b);
int q;
scanf("%d", &q);
while(q--) {
int x, y;
scanf("%d %d", &x, &y);
printf("%d\n", get_distance(x, y));
}
return 0;
}
*/
