#include <bits/stdc++.h>

using namespace std;

constexpr int N = 2e5 + 10;

int n, m, ans;
string s, t;

inline void change() {for (char &i : s) i = '0' + '1' - i;}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(nullptr), cout.tie(nullptr);
    cin >> s >> t; n = s.length(), m = t.length();
    if (m == 1) ans = s.find(t) == s.npos ? 0 : -1;
    else if (m == 2) {
        if (t == "00") {
            if (count(s.begin(), s.end(), '0') > (n + 1) / 2) ans = -1;
            else for (int i = 1; i < n; i++) ans += (s[i] == s[i - 1] && s[i] == '0');
        }
        if (t == "10") change();
        for (int i = 1; i < n; i++) ans += (s[i] != s[i - 1] && s[i] == '1');
    } else if (m == 3) {
        if (t == "010" || t == "101") {
            if (t == "101") change();
            for (int i = 1; i < n - 1; i++) ans += (s[i - 1] != s[i] && s[i] != s[i + 1] && s[i] == '1');
        } else if (t == "000" || t == "111") {
            if (t == "111") change();
            if (count(s.begin(), s.end(), '1') * 3 + 2 < n) ans = 0;
            else {
                int c2 = 0;
                for (int i = 1; i < n; i++) c2 += (s[i] == '1' && s[i - 1] == '1');
                c2 += (s[0] == '1') + (s[n - 1] == '1'), s[n] = '1';
                for (int i = 0, cnt = 0; i <= n; i++) {
                    if (s[i] == '0') cnt++;
                    else {
                        if (cnt <= 2) {cnt = 0; continue;}
                        else {
                            ans += (cnt - 1) / 2;
                            int tmp = min(c2, cnt / 2 - 1);
                            c2 -= tmp, ans += max(0, cnt / 2 - 1 - tmp), cnt = 0;
                        }
                    }
                }
            }
        } else {
            if (count(t.begin(), t.end(), '0') == 1) change();
            if (t[0] == '1') reverse(s.begin(), s.end());
            for (int i = 0, cnt = 0; i < n; i++) {
                if (s[i] == '0') cnt++;
                else ans += (cnt >= 2), cnt = 0;
            }
        }
    }
    cout << ans;
    return 0;
}