#include <bits/stdc++.h>
#include <math.h>

using namespace std;

// c++ short types
#define vt vector
typedef long long ll;
typedef long double ld;

void whattime() { cout << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl; }

const ll inf = 1e18;

void solve() {
	string s, t;
	cin >> s >> t;
	if(accumulate(s.begin(), s.end(), 0) - s.size() * 'a' < accumulate(t.begin(), t.end(), 0) - t.size() * 'a') {
		cout << "-1\n";
		return ;
	}
	auto Get1 = [](int k) {
		return 1 << min(k, 22);
	};
	auto Get2 = [](int k) {
		return (1 << min(k, 22)) - 1;
	};
	const int amax = 2e5;
	auto f = [&](int k) {
		int need = 0, j = 0;
		for(int i = 0; i < (int)t.size(); ++i) {
			if(t[i] == 'b') {
				int have = 0;
				bool flag = false;
				while(j  < (int)s.size()) {
					if(s[j] == 'a') {
						have += Get1(k);
					} else {
						have += Get2(k);
					}
					have = min(have, amax);
					if(have >= need && s[j] == 'b') {
						flag = 1;
						++j;
						break;
					}
					++j;
				}
				need = 0;
				if(!flag) {
					return false;
				}
			} else {
				++need;
			}
		}
		int have = 0;
		for(int i = j; i < (int)s.size(); ++i) {
			if(s[i] == 'a') {
				have += Get1(k);
			} else {
				have += Get2(k);
			}
			have = min(have, amax);
		}
		return have >= need;
	};
	int l = -1, r = 20;
	while(r - l > 1) {
		int m = (l + r) >> 1;
		if(f(m)) {
			r = m;
		} else {
			l = m;
		}
	}
	cout << r << "\n";
}

int main()
{
	int tt = 1;
	for(int t = 0; t < tt; ++t) {
		solve();
	}
	return 0;
}