#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--)
#define all(a) a.begin(), a.end()
#define pb emplace_back

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;
    }
    else 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;
    }
    else if(T.size() == 2 && T[0] == T[1]){
        ll cnt = 0;
        ll ans = 0;
        rep(i,0,N){
            if(S[i] == T[0]){
                cnt++;
                if(i && S[i-1] == T[0]) ans++;
            }
        }
        if(cnt*2 > N+1){
            cout << -1 << ln;
            return 0;
        }
        cout << ans << ln;
    }
    else if(T.size() == 3 && T[0] != T[2]){
        if(T[0] != T[1]){
            reverse(all(S));
            reverse(all(T));
        }
        assert(T[0] == T[1]);
        ll ans = 0;
        ll cnt = 0;
        bool flag = false;
        per(i,N-1,0){
            if(S[i] == T[2]) flag = true;
            if(flag){
                if(S[i] == T[0]) cnt++;
                else{
                    if(cnt > 1) ans++;
                    cnt = 0;
                }
            }
        }
        if(cnt > 1) ans++;
        cout << ans << ln;
    }
    else if(T.size() == 3 && T[0] != T[1]){
        assert(T[0] == T[2]);
        // 010101010101010 7
        // 010110101010010 5
        ll cnt = 0;
        rep(i,2,N){
            if(S[i-2] == T[0] && S[i-1] == T[1] && S[i] == T[2]) cnt++;
        }
        ll ans = (cnt+1)/2;
        cout << ans << ln;
    }
    else{
        assert(T.size() == 3 && T[0] == T[1] && T[1] == T[2]);
        ll cnt = 0;
        std::priority_queue<ll> que;
        ll remain = 0;
        ll total = 0;
        per(i,N-1,0){
            if(S[i] == T[0]) cnt++, total++;
            else{
                if(cnt) que.push(cnt);
                cnt = 0;
            }
            if(S[i] != T[0] && i && S[i-1] != T[0]) remain++;
        }
        if(N < 3){
            cout << 0 << ln;
            return 0;
        }
        if(N-N/3 < total){
            cout << -1 << ln;
            return 0;
        }
        if(S[0] != T[0]) remain++;
        if(S[N-1] != T[0]) remain++;
        if(cnt) que.push(cnt);
        ll ans = 0;
        while(!que.empty() && remain){
            ll el = que.top(); que.pop();
            if(el <= 2) break;
            ans++;
            remain--;
            que.push(el-2);
        }
        while(!que.empty()){
            ll el = que.top(); que.pop();
            ans += std::max(0ll, el-2);
        }
        cout << ans << ln;
    }
}