#include<iostream>
#include<cstring>
#include<vector>
using namespace std;
using LL = long long;

vector<int> z_algorithm(const string &s){
    int n = s.size();
    vector<int> a(n);
    a[0] = n;
	for(int i = 1, l = 0, r = 0; i < n; i++){
		if (i <= r) a[i] = min(a[i - l], r - i + 1);
		while(i + a[i] < n && s[i + a[i]] == s[a[i]]) ++a[i];
		if (i + a[i] - 1 > r) l = i, r = i + a[i] - 1;
	}
    return a;
}


int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    string s, t;
    cin >> s >> t;
    if (t == string(t.size(), 'a')){
        int ans = 1e9;
        {
            int cnt = 0;
            int len = 0;
            while(len < t.size()){
                cnt += 1;
                len = len * 2 + 1;
            }
            ans = min(ans, cnt);
        }
        for(int i = 0; i < s.size(); i++){
            if (s[i] == 'b') continue;
            int j = i;
            while(j + 1 < s.size() and s[j + 1] == 'a') j++;
            int len = j - i + 1;
            int cnt = 0;
            while(len < t.size()){
                len = len * 2 + (j + 1 != s.size());
                cnt += 1;
            }
            ans = min(ans, cnt);
            i = j;
        }
        cout << ans << '\n';
        return 0;
    }    
    for(int i = 0; i < 19; i++){
        vector<int> bad(1 << i);
        for(int j = 0; j < t.size(); j++){
            if (t[j] == 'b'){
                bad[j % (1 << i)] = 1;
            }
        }
        vector<int> v;
        for(int j = 0; j < 1 << i; j++){
            if (bad[j]){
                v.push_back(j);
            }
        }
        if (v.size() > 1) continue;
        int st = v[0];
        string str;
        for(int j = st; j < t.size(); j += (1 << i)){
            str += t[j];
        }
        auto z = z_algorithm(str + " " + s);
        for(int j = str.size() + 1; j < z.size(); j++){
            if (z[j] >= str.size()){
                if (j + 1 != z.size() or st + 1 == (1 << i)){
                    cout << i << '\n';
                    return 0;
                }
            }   
        }
    }
    cout << -1 << '\n';

}