#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int mxN=1e5;
int p[mxN+1][3], bad[mxN+1];
void init(string a, string b) {
int n=a.size();
for (int i=0; i<n; ++i) {
p[i+1][0]=p[i][0]+(a[i]=='A')-(b[i]=='A');
p[i+1][1]=p[i][1]+(a[i]=='T')-(b[i]=='T');
p[i+1][2]=p[i][2]+(a[i]=='C')-(b[i]=='C');
bad[i+1]=bad[i]+(a[i]!=b[i]);
}
}
int get_distance(int x, int y) {
for (int i=0; i<3; ++i)
if (p[y+1][i]-p[x][i])
return -1;
return (bad[y+1]-bad[x]+1)/2;
}
/*int main() {
ios::sync_with_stdio(0);
cin.tie(0);
init("ATACAT", "ACTATA");
cout << get_distance(1, 3) << " " << get_distance(4, 5) << " " << get_distance(3, 5);
return 0;
}*/
