#include <iostream>
#include <algorithm>
#include <cstring>

typedef long long ll;
typedef double lf;

// #define DEBUG 1
struct IO
{
    #define MAXSIZE (1 << 20)
    #define isdigit(x) (x >= '0' && x <= '9')
    char buf[MAXSIZE], *p1, *p2;
    char pbuf[MAXSIZE], *pp;
    #if DEBUG
    #else
    IO() : p1(buf), p2(buf), pp(pbuf) {}
    ~IO() {fwrite(pbuf, 1, pp - pbuf, stdout);}
    #endif
    #define gc() (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, MAXSIZE, stdin), p1 == p2) ? ' ' : *p1++)
    #define blank(x) (x == ' ' || x == '\n' || x == '\r' || x == '\t')

    template <typename T>
    void Read(T &x)
    {
        #if DEBUG
        std::cin >> x;
        #else
        bool sign = 0; char ch = gc(); x = 0;
        for (; !isdigit(ch); ch = gc())
            if (ch == '-') sign = 1;
        for (; isdigit(ch); ch = gc()) x = x * 10 + (ch ^ 48);
        if (sign) x = -x;
        #endif
    }
    void Read(char *s)
    {
        #if DEBUG
        std::cin >> s;
        #else
        char ch = gc();
        for (; blank(ch); ch = gc());
        for (; !blank(ch); ch = gc()) *s++ = ch;
        *s = 0;
        #endif
    }
    void Read(char &c) {for (c = gc(); blank(c); c = gc());}

    void Push(const char &c)
    {
        #if DEBUG
        putchar(c);
        #else
        if (pp - pbuf == MAXSIZE) fwrite(pbuf, 1, MAXSIZE, stdout), pp = pbuf;
        *pp++ = c;
        #endif
    }
    template <typename T>
    void Write(T x)
    {
        if (x < 0) x = -x, Push('-');
        static T sta[35];
        int top = 0;
        do sta[top++] = x % 10, x /= 10; while (x);
        while (top) Push(sta[--top] ^ 48);
    }
    template <typename T>
    void Write(T x, char lst) {Write(x), Push(lst);}
} IO;
#define Read(x) IO.Read(x)
#define Write(x, y) IO.Write(x, y)
#define Put(x) IO.Push(x)

using namespace std;

const int MAXN = 2e5 + 10;

int n, m;
char s[MAXN], t[4];
int cnt0, cnt1;

inline void Flip()
{
    for (int i = 1; i <= n; i++) s[i] = (s[i] == '0' ? '1' : '0');
    for (int i = 1; i <= m; i++) t[i] = (t[i] == '0' ? '1' : '0');
}

inline void Solution1()
{
    bool flag = 1;
    for (int i = 1; i <= n; i++)
        if (s[i] == '0') {flag = 0; break;}
    if (flag) cout << "0\n";
    else cout << "-1\n";
}

inline void Solution2_1()
{
    if (cnt0 > cnt1 + 1) return cout << "-1\n", void();
    int ans = 0;
    for (int i = 1; i < n; i++)
        if (s[i] == '0' && s[i + 1] == '0') ans++;
    cout << ans << "\n";
}

inline void Solution2_2()
{
    int ans = 0;
    for (int i = 2; i <= n; i++)
        if (s[i - 1] == '0' && s[i] == '1') ans++;
    cout << ans << "\n";
}

int a[MAXN], top;

inline void Solution3_1()
{
    if (cnt0 > cnt1 * 2 + 2) return cout << "-1\n", void();
    int sum = 0;
    for (int i = 1; i <= n; i++)
        if (s[i] == '1') a[++top] = sum, sum = 0;
        else sum++;
    a[++top] = sum;
    cnt0 = cnt1 = 0;
    for (int i = 1; i <= top; i++) cnt0 += (a[i] == 0), cnt1 += (a[i] == 1);
    int ans = 0;
    for (int i = 1; i <= top; i++)
        if (a[i] > 1)
        {
            while (a[i] > 2)
            {
                if (cnt0) a[i] -= 2, cnt0--;
                else a[i]--, cnt1--;
                ans++;
            }
        }
    cout << ans << "\n";
}

inline void Solution3_2()
{
    int ans = 0;
    for (int i = 2; i < n; i++)
        if (s[i - 1] == '0' && s[i] == '1' && s[i + 1] == '0')
            ans++;
    cout << (ans + 1) / 2 << "\n";
}

inline void Solution3_3()
{
    if (t[2] == '1') reverse(s + 1, s + n + 1), Flip();
    int ans = 0;
    for (int i = 3; i <= n; i++)
        if (s[i] == '1' && s[i - 1] == '0' && s[i - 2] == '0')
            ans++;
    cout << ans << "\n";
}

int main()
{
    // freopen("A.in", "r", stdin);
    // freopen("A.out", "w", stdout);
    #if DEBUG
    #else
    ios::sync_with_stdio(0), cin.tie(0);
    #endif
    Read(s + 1), Read(t + 1), n = strlen(s + 1), m = strlen(t + 1);
    if (n < m) return cout << "0\n", 0;
    if (t[1] == '1') Flip();
    for (int i = 1; i <= n; i++) cnt0 += (s[i] == '0'), cnt1 += (s[i] == '1');

    if (m == 1) Solution1();
    else if (m == 2 && t[1] == t[2]) Solution2_1();
    else if (m == 2) Solution2_2();
    else if (m == 3 && t[1] == t[2] && t[2] == t[3]) Solution3_1();
    else if (m == 3 && t[1] == t[3]) Solution3_2();
    else Solution3_3();
    return 0;
}