#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){
    return -1;
}
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);
    out(res);
}