#include <iostream>
#include <vector>
struct Count {
int at, ca, tc;
int qw;
Count() : at(0), ca(0), tc(0), qw(0) {}
inline Count operator-(Count rhs) const {
Count result = *this;
result.at -= rhs.at;
result.ca -= rhs.ca;
result.tc -= rhs.tc;
result.qw -= rhs.qw;
return result;
}
};
std::vector<Count> prefixes;
void init(std::string a, std::string b) {
prefixes.reserve(a.size() + 1);
Count count;
prefixes.push_back(count);
for (size_t i = 0; i < a.size(); i++) {
if (a[i] == 'A' && b[i] == 'T') count.at += 1;
if (a[i] == 'T' && b[i] == 'A') count.at -= 1;
if (a[i] == 'C' && b[i] == 'A') count.ca += 1;
if (a[i] == 'A' && b[i] == 'C') count.ca -= 1;
if (a[i] == 'T' && b[i] == 'C') count.tc += 1;
if (a[i] == 'C' && b[i] == 'T') count.tc -= 1;
if (a[i] != b[i]) count.qw += 1;
prefixes.push_back(count);
}
}
int get_distance(int x, int y) {
y += 1;
Count count = prefixes[y] - prefixes[x];
if (!(count.at == count.ca && count.ca == count.tc)) return -1;
return (count.qw + std::abs(count.at)) / 2;
}
