#include <iostream>
#include <string>
#include <algorithm>
#include <set>
using namespace std;

string s, t;
set<int> pos[30];

int main() {
	cin >> s >> t;
	for (int i = 0; i < s.size(); i++) pos[s[i] - 'a'].insert(i);
	int a = 0, b = 0;
	for (int i = 0; i < t.size(); i++) {
		if (pos[t[i] - 'a'].empty()) {
			cout << -1 << endl;
			return 0;
		}
		if (pos[t[i] - 'a'].lower_bound(b) == pos[t[i] - 'a'].end()) {
			a++;b=0;
		}
		b = *(pos[t[i] - 'a'].lower_bound(b));
		b++;
	}
	cout<<a*s.size()+b<<endl;
}