#include <bits/stdc++.h>
#ifdef dbg
#define D(...) fprintf(stderr, __VA_ARGS__)
#define DD(...) D(#__VA_ARGS__ " = "), debug_helper::debug(__VA_ARGS__), D("\n")
#include "C:\Users\wsyear\Desktop\OI\templates\debug.hpp"
#else
#define D(...) ((void)0)
#define DD(...) ((void)0)
#endif
#define rep(i, j, k) for (int i = (j); i <= (k); ++i)
#define per(i, j, k) for (int i = (j); i >= (k); --i)
#define SZ(v) int((v).size())
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
using ll = long long;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;

using namespace std;

const int N = 200010;

int n, m, a[N];
string str;
priority_queue<int> q;

int A(int x) {
  int cnt = 0;
  rep (i, 1, n) if (a[i] == x) cnt++;
  return cnt ? -1 : 0;
}

int AA(int x) {
  int cnt = 0;
  rep (i, 1, n) if (a[i] == x) cnt++;
  if (cnt > (n + 1) / 2) return -1;
  for (int l = 1, r; l <= n; l = r + 1) {
    if (a[l] != x) r = l;
    else {
      r = l;
      while (r < n && a[r + 1] == x) r++;
      cnt--;
    }
  }
  return cnt;
}

int AB(int x) {
  int cnt = 0;
  for (int r = n - 1, l; r >= 1; r = l - 1) {
    if (a[r] != x) l = r;
    else {
      l = r;
      while (l > 1 && a[l - 1] == x) l--;
      cnt++;
    }
  }
  return cnt;
}

int AAB(int x) {
  int cnt = 0;
  for (int r = n - 1, l; r >= 1; r = l - 1) {
    if (a[r] != x) l = r;
    else {
      l = r;
      while (l > 1 && a[l - 1] == x) l--;
      cnt += (r > l);
    }
  }
  return cnt;
}

int ABA(int x) {
  int cnt = 0;
  for (int r = n, l; r >= 1; r = l - 1) {
    if (a[r] == x) l = r;
    else {
      l = r;
      while (l > 1 && a[l - 1] != x) l--;
      cnt += (r == l && l > 1 && r < n);
    }
  }
  return (cnt + 1) / 2;
}

int AAA(int x) {
  int cnt = 0;
  rep (i, 1, n) if (a[i] == x) cnt++;
  if (cnt > n / 3 * 2 + n % 3) return -1;
  int c1 = 0, c2 =0;
  while (!q.empty()) q.pop();
  for (int l = 1, r; l <= n; l = r + 1) {
    r = l;
    while (r < n && a[r + 1] == a[r]) r++;
    if (a[l] != x) c2 += r - l;
    else if (l == r) c1 += 1;
    else if (r - l > 1) q.push(r - l - 1);
  }
  int ans = 0;
  while (!q.empty()) {
    int x = q.top();
    q.pop();
    if (c2) {
      if (x >= 2) c2--, x -= 2;
      else c2--, c1++, x = 0;
    } else {
      c1--, x -= 1;
    }
    ans++;
    if (x != 0) q.push(x);
  }
  return ans;
}

void work() {
  cin >> str, n = str.length();
  rep (i, 1, n) a[i] = str[i - 1] - '0';
  cin >> str, m = str.length();
  if (m == 1) cout << A(str[0] - '0') << '\n';
  else if (m == 2 && str[0] == str[1]) cout << AA(str[0] - '0') << '\n';
  else if (m == 2 && str[0] != str[1]) cout << AB(str[0] - '0') << '\n';
  else if (str[0] == str[1] && str[1] != str[2]) cout << AAB(str[0] - '0') << '\n';
  else if (str[0] != str[1] && str[1] == str[2]) reverse(a + 1, a + n + 1), cout << AAB(str[2] - '0') << '\n';
  else if (str[0] == str[2] && str[0] != str[1]) cout << ABA(str[0] - '0') << '\n';
  else if (str[0] == str[1] && str[1] == str[2]) cout << AAA(str[0] - '0') << '\n';
}

int main() {
  // freopen("shin.in", "r", stdin);
  // freopen("shin.out", "w", stdout);
  cin.tie(nullptr) -> ios::sync_with_stdio(false);
  int t = 1;
  while (t--) work();
}