#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1e6 + 10;
int n;
char s[N], t[N];
void solve() {
scanf("%s%s", t + 1, s + 1);
n = strlen(s + 1);
int ans = 0;
for (int i = 2; i < n; i ++ )
if (s[i] != t[i] && s[i - 1] == s[i + 1] && s[i - 1] != s[i])
ans ++ , s[i] ^= 1;
if (strcmp(s + 1, t + 1)) ans = -1;
printf("%d\n", ans);
}
int main() {
int _; scanf("%d", &_);
while (_ -- ) solve();
return 0;
}
太棒了