/*#pragma GCC optimize("O3")
#pragma GCC optimization("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")*/
#include <bits/stdc++.h>
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>*/
#define ll long long
#define ll1 long long
#define ull unsigned long long
#define dou long double
#define str string
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll, ll>
#define vpll vector<pair<ll, ll>>
#define vbool vector<bool>
#define vstr vector<str>
#define vvll vector<vll>
#define pb push_back
#define pf push_front
#define endl "\n"
#define fr first
#define se second
// #define sortcmp(a) sort(a.begin(), a.end(), cmp)
#define sort(a) sort(a.begin(), a.end())
#define reverse(a) reverse(a.begin(), a.end())
#define speed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define ordered_set tree<ll, null_type, less_equal<ll>, rb_tree_tag, tree_order_statistics_node_update>
using namespace std;
//using namespace __gnu_pbds;
const ll INF = 1e18+7;
const int lg = 20;
//const ll MOD = 1e9+7;
//const ll MOD2 = 998244353;
const ll MOD3 = 1e6+3;
mt19937 rng(1488);
ll randll(ll l, ll r) {
return uniform_int_distribution<ll>(l, r)(rng);
}
int main() {
speed;
str s, s1;
cin >> s;
cin >> s1;
if (s1.size() == 1) {
sort(s);
if (str(1, s[0]) == s1 || str(1, s[s.size()-1]) == s1) cout << -1 << endl;
else cout << 0 << endl;
}
else if (s1.size() == 2 && s1[0] != s1[1]){
if (s1[0] == '0') reverse(s);
ll k = 0;
for (int i = 0; i < s.size(); i ++) {
if (s[i] == '0') continue;
if (i == 0 || s[i-1] == '0') k ++;
}
if (s[s.size()-1] == '1') k --;
cout << k << endl;
}
else if (s1.size() == 2) {
if (s1[0] == '1') {
s1[0] = s1[1] = '0';
for (int i = 0; i < s.size(); i++) {
if (s[i] == '0') s[i] = '1';
else s[i] = '0';
}
}
ll k = 0, k1 = 0, c = 0, c1 = 0;
for (int i = 0; i < s.size(); i ++) {
if (s[i] == '1') {
k1 ++;
c += max((ll)0, k-1);
k = 0;
}
else {
k ++;
if (i-k1 != 0) k1 --;
if (k1 >= 0)c1 += k1;
k1 = 0;
}
}
c += max((ll)0, k-1);
c1 += k1;
//cout << c1 << ' ' << c << endl;
if (c1 < c) cout << -1 << endl;
else cout << c << endl;
}
}
