#include "dna.h"
#include <bits/stdc++.h>
// #include <ext/rope>
// #include <ext/pb_ds/assoc_container.hpp>
// using namespace __gnu_pbds;
// using namespace __gnu_cxx;
using namespace std;
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define ll long long
#define ull unsigned long long
#define ld long double
#define pb push_back
#define bit(mask, i) ((mask >> i) & 1)
#define el '\n'
#define F first
#define S second
template <class X, class Y> bool maximize(X &x, const Y &y) { return (x < y ? x = y, 1 : 0); }
template <class X, class Y> bool minimize(X &x, const Y &y) { return (x > y ? x = y, 1 : 0); }
const int INF = 1e9;
const ll LINF = 1e18;
const int MOD = 1e9 + 7;
const int MULTI = 0;
const ld eps = 1e-9;
const int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0}; // R D L U
const int ddx[4] = {-1, 1, 1, -1}, ddy[4] = {1, 1, -1, -1}; // UR DR DL UL
const char cx[4] = {'R', 'D', 'L', 'U'};
const ll base = 31;
const int nMOD = 2;
const ll mods[] = {(ll)1e9 + 10777, (ll)1e9 + 19777, (ll)1e9 + 3, (ll)1e9 + 3777};
const int MAX = 1e5 + 5;
int n, prefDiff[MAX], prefS[MAX], prefT[MAX];
string s, t;
void init(string a, string b) {
n = (int) a.size();
s = ' ' + a; t = ' ' + b;
for (int i = 1; i <= n; ++i) {
prefDiff[i] = prefDiff[i - 1] + (s[i] != t[i]);
prefS[i] = prefS[i - 1] + (s[i] == 'A');
prefT[i] = prefT[i - 1] + (t[i] == 'A');
}
}
int get_distance(int x, int y) {
++x; ++y;
int s = prefDiff[y] - prefDiff[x - 1];
if (s % 2 == 0 && prefS[y] - prefS[x - 1] == prefT[y] - prefT[x - 1])
return s / 2;
return -1;
}
