#include "dna.h"
#include <bits/stdc++.h>
using namespace std;
const int mxN = 1e5 + 123;
int pref[mxN];
int cntA[mxN][3], cntB[mxN][3], N;
map<char, int> m = {{'A', 0}, {'C', 1}, {'T', 2}};
void init(string a, string b)
{
//Say a is the 'original'
assert(a.size() == b.size());
N = a.size();
for(int i = 0; i < N;i++)
{
for(int j = 0; j < 3;j++)
{
cntA[i+1][j] = cntA[i][j];
cntB[i+1][j] = cntB[i][j];
}
++cntA[i+1][m[a[i]]];
++cntB[i+1][m[b[i]]];
pref[i+1] = pref[i] + (a[i] != b[i]);
}
}
int get_distance(int L, int R)
{
++R;
bool ok = 1;
for(int i = 0; i < 3;i++)
if(cntA[R][i] - cntA[L][i] != cntB[R][i] - cntB[L][i])
ok = 0;
if(!ok) return -1;
int bad = pref[R] - pref[L];
return (bad + 1) / 2;
}
/*
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
string s, t;
cin >> s >> t;
init(s, t);
int Q;
cin >> Q;
while(Q--)
{
int a, b;
cin >> a >> b;
cout << get_distance(a, b) << "\n";
}
}
*/
