#include <bits/stdc++.h>
// #include "atcoder/modint"

using i64 = long long;
// using Fp = atcoder::modint998244353;

int solve(std::string S, std::string T) {
    const int N = (int)S.size();
    if (T.size() == 1) {
        const auto s = std::count(S.begin(), S.end(), T[0]);
        return s ? -1 : 0;
    }
    std::vector<std::pair<char, int>> P;
    {
        int last = 0;
        for (int i = 0; i < N; ++i) {
            if (S[i] != S[last]) {
                P.push_back({S[last], i - last});
                last = i;
            }
        }
        P.push_back({S[last], N - last});
    }
    const int U = (int)P.size();
    if (T.size() == 2 and T[0] != T[1]) {
        i64 ans = 0;
        for (int i = 0; i < U; ++i) {
            if (i != 0 and P[i].first == T[1]) ++ans;
        }
        return ans;
    } else if (T.size() == 2) {
        int cnta = 0, cntb = 0;
        for (const auto e : S) {
            if (e == T[0]) ++cnta;
            else ++cntb;
        }
        if (cntb + 1 < cnta) {
            return -1;
        } else {
            int ans = 0;
            for (int i = 0; i < N - 1; ++i) {
                if (S[i] == S[i + 1] and S[i] == T[0]) ++ans;
            }
            return ans;
        }
        return 0;
    }

    assert(T.size() == 3);
    if (T[0] != T[2]) {
        if (T[1] == T[2]) {
            std::reverse(T.begin(), T.end());
            std::reverse(S.begin(), S.end());
            std::reverse(P.begin(), P.end());
        }
        if (T[0] == '1') {
            for (auto &e : S) {
                if (e == '0') e = '1';
                else e = '0';
            }
            for (auto &e : T) {
                if (e == '0') e = '1';
                else e = '0';
            }
            for (auto &[e, len] : P) {
                if (e == '0') e = '1';
                else e = '0';
            }
        }
        int ans = 0;
        for (int i = 0; i < N - 2; ++i) {
            if (S.substr(i, 3) == T) {
                ++ans;
            }
        }
        return ans;
    }
    if (T[0] != T[1]) {
        assert(T[0] == T[2] and T[0] != T[1]);
        if (T[0] == '1') {
            for (auto &e : S) {
                if (e == '0') e = '1';
                else e = '0';
            }
            for (auto &e : T) {
                if (e == '0') e = '1';
                else e = '0';
            }
            for (auto &[e, len] : P) {
                if (e == '0') e = '1';
                else e = '0';
            }
        }
        int cnt = 0;
        for (int i = 0; i < U; ++i) {
            if (i != 0 and i != U - 1 and P[i].first == T[1] and P[i].second == 1) ++cnt;
        }
        return (cnt + 1) / 2;
        return 0;
    } else {
        assert(T[0] == T[1] and T[1] == T[2]);
        int cnta = 0, cntb = 0;
        for (int i = 0; i < N; ++i) {
            if (S[i] == T[0]) ++cnta;
            else ++cntb;
        }
        if (cntb * 2 + 2 < cnta) {
            return -1;
        }

        int cntx = 0, cnty = 0, capx = 0, capy = 0;
        for (int i = 0; i < U; ++i) {
            if (P[i].first != T[0]) continue;
            if (P[i].second % 2 == 0) {
                ++cntx;
                capx += P[i].second;
            } else {
                ++cnty;
                capy += P[i].second;
            }
        }

        int ans = capx / 2 - cntx + capy / 2 - cnty / 2;
        return ans;
    }
    return -1;
}


int main() {
    std::string S, T;
    std::cin >> S >> T;
    std::cout << solve(S, T) << std::endl;
}