#include <bits/stdc++.h>
using namespace std;
#define all(a) begin(a), end(a)

/*
    0 => jimei
    00 => 00 wo kirihanasu
    haji no 1 wo yoseru
     or 11 wo kirihanasu
    01 => 11111000000
     hidari no 0 to migi no 1 de reverse
    000 => 000+ wo kirihanasu
    1 ga tarinaku naru toki ha kisuu ko no 0 wo kuttukeru
    001 => 1111101101010111000000
     00+ wo migi ni
    010 => 111111001101110001100111111
     chuuou no 1 to 1 wo kuttukeru
*/
int count(const string& S, char c) {
    return count(all(S), c);
}
string reversed(string S) {
    reverse(all(S));
    return S;
}
int solve() {
    string S, T;
    cin >> S >> T;
    const int N = S.size();
    if(count(T, '1') > count(T, '0')) {
        for(char& c : S) c ^= 1;
        for(char& c : T) c ^= 1;
    }
    if(T > reversed(T)) {
        S = reversed(S);
        T = reversed(T);
    }
    if(T == "0") {
        if(count(S, '0')) return -1;
        return 0;
    }
    if(T == "01") {
        int ans = 0;
        for(int i = 0; i + 1 < N; i++) if(S.substr(i, 2) == "01") ans++;
        return ans;
    }
    return 0;
}
int main() {
    cout << solve() << endl;
}