#include <bits/stdc++.h>
using std::cin;
using std::cout;
using std::vector;
using std::string;
using ll = long long;
using vi = vector<ll>;
using vii = vector<vi>;
using pii = std::pair<ll,ll>;

#define ln "\n"
#define rep(i,j,k) for(ll i=ll(j); i<ll(k); i++)
#define REP(i,j,k) for(ll i=ll(j); i<=ll(k); i++)
#define per(i,j,k) for(ll i=ll(j); i>=ll(k); i--)

int main(){
    string S, T; cin >> S >> T;
    ll N = S.size();
    if(T.size() == 1){
        ll ans = 0;
        rep(i,0,N){
            if(S[i] == T[0]) ans = -1;
        }
        cout << ans << ln;
    }
    if(T.size() == 2 && T[0] != T[1]){
        ll cnt = 1;
        rep(i,1,N){
            if(S[i-1] != S[i]) cnt++;
        }
        ll ans = 0;
        if(S[0] == T[0]) ans = cnt/2;
        else ans = (cnt-1)/2;
        cout << ans << ln;
    }
}