//  ↘ ⬇ ⬇ ⬇ ⬇ ⬇ ↙
//  ➡ @roadfromroi ⬅
//  ↗ ⬆ ⬆ ⬆ ⬆ ⬆ ↖
#include <iostream>
#include "vector"
#include "algorithm"
#include "numeric"
#include "climits"
#include "iomanip"
#include "bitset"
#include "cmath"
#include "map"
#include "deque"
#include "array"
#include "set"
#define all(x) x.begin(), x.end()
using namespace std;
int get0(string s) {
    for (auto i : s) {
        if (i == '0')
            return -1;
    }
    return 0;
}
int get00(string s) {
    vector<int> ema;
    int cr = 0;
    for (auto i : s) {
        if (i == '1') {
            ema.push_back(cr);
            cr = 0;
        } else {
            cr++;
        }
    }
    ema.push_back(cr);
    sort(all(ema));
    int sm = 0;
    for (auto i : ema)
        sm += i;
    if (ema.size() < sm)
        return -1;
    int res = 0;
    for (auto i : ema) {
        if (i > 1)
            res += i - 1;
    }
    return res;
}
int get01(string s) {
    char prv = '?';
    int res = 0;
    for (auto i : s) {
        if (i == prv)
            continue;
        if (prv != '?' and i == '1')
            res++;
        prv = i;
    }
    return res;
}
void solve() {
    string s, t;
    cin >> s >> t;
    int cn = 0;
    for (auto i : t) {
        if (i == '0')
            cn++;
        else
            cn--;
    }
    if (cn < 0) {
        for (auto &i : t) {
            i = '1' - i + '0';
        }
        for (auto &i : s) {
            i = '1' - i + '0';
        }
    }
    if (t[0] != '0') {
        reverse(all(t));
        reverse(all(s));
    }
    if (t == "0") {
        cout << get0(s) << '\n';
    }
    if (t == "00") {
        cout << get00(s) << '\n';
    }
    if (t == "01") {
        cout << get01(s) << '\n';
    }
}
signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int t = 1;
    while (t--) {
        solve();
    }
}