#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef vector<P> vp;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,k,n) for(ll i=(ll)(k);i<(ll)(n);i++)
#define all(a) a.begin(),a.end()
#define pb emplace_back
#define fi first
#define se second
#define rsort(a) {sort(all(a));reverse(all(a));}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}

ll sol1(ll n,string s,string t){
    rep(i,n)if(s[i]==t[0])return -1;
    return 0;
}
ll sol2(ll n,string s,string t){
    vi v;
    for(char c:s){
        if(v.size()==0||v.back()!=c-'0')v.pb(c-'0');
    }
    n=v.size();
    ll ans=n/2;
    if(n%2==0&&v[0]==t[1]-'0')ans--;
    return ans;
}
ll sol3(ll n,string s,string t){
    ll cnt=0,ans=0;
    for(char c:s)if(c==t[0])cnt++;
    if(cnt*2>=n+2)return -1;
    rep(i,n-1)if(s[i]==s[i+1]&&s[i]==t[0])ans++;
    return ans;
}
ll sol4(ll n,string s){
    vp v;
    for(char c:s){
        if(v.size()==0||v.back().fi!=c-'0')v.pb(c-'0',1);
        else v.back().se++;
    }
    ll ans=0;
    for(int i=1;i<v.size();i++)if(v[i].fi==0&&v[i].se>1)ans++;
    return ans;
}
ll sol5(ll n,string s,string t){
    ll ans=0;
    rep(i,n-2)if(s[i]==t[0]&&s[i+1]==t[1]&&s[i+2]==t[2])ans++;
    return (ans+1)/2;
}
ll sol6(ll n,string s,string t){
    ll ans=0,cnt=0;
    rep(i,n)if(s[i]==t[0])cnt++;
    if(cnt+(cnt-1)/2>n)return -1;
    vp v;
    for(char c:s){
        if(v.size()==0||v.back().fi!=c-'0')v.pb(c-'0',1);
        else v.back().se++;
    }
    for(auto x:v)if(x.fi==t[0]-'0'&&x.se>2){
        ans+=(x.se-1)/2;
    }
    return ans;
}
int main(){
    string s,t;cin>>s>>t;
    ll n=s.size();
    ll res=-1;
    if(t.size()==1)res=sol1(n,s,t);
    else if(t.size()==2&&t[0]!=t[1])res=sol2(n,s,t);
    else if(t.size()==2)res=sol3(n,s,t);
    else if(t[0]!=t[2]){
        string tmp;
        if(t=="110"){
            for(int i=n-1;i>=0;i--)tmp+='0'+1-(s[i]-'0');
        }
        if(t=="011"){
            rep(i,n)tmp+='0'+1-(s[i]-'0');
        }
        if(t=="001"){
            for(int i=n-1;i>=0;i--)tmp+=s[i];
        }
        if(t=="100"){
            tmp=s;
        }
        res=sol4(n,tmp);
    }
    else if(t[0]!=t[1]){
        res=sol5(n,s,t);
    }
    else res=sol6(n,s,t);
    out(res);
}