#include <iostream>

#include <string>

using namespace std;

const int MAX_LETTER = 26;

int main()

{

    string source;

    string target;

    cin>>source;

    cin>>target;

    int cnt[MAX_LETTER] = {0};

    for (int i = 0; target[i] != '\0'; i++) {

        cnt[target[i] - 'a'] = 1;

    }

    for (int i = 0; source[i] != '\0'; i++) {

        cnt[source[i] - 'a'] = 0;

    }

    for (int i = 0; i < MAX_LETTER;i++) {

        if (cnt[i] == 1) {

            cout<< "-1" <<endl;

            return 0;

        }

    }

    int t = 0;

    int i = 0;

    int j = 0;

    while (target[i]) {

        t++;

        j = 0;

        while (target[i] && source[j]) {

            if (target[i] == source[j]) {

                i++;

                j++;

            } else {

                j++;

            }

        }

    }

    cout<<t<<endl;

    return 0;

}