#include <bits/stdc++.h>
using namespace std;
long long int gcd(long long int a, long long int b) {
  if (b < a) {
    long long int temp = a;
    a = b;
    b = temp;
  }
  if (a == 0) {
    return b;
  }
  return gcd(b % a, a);
}
long long int lcm(long long int a, long long int b) {
  return (a * b / gcd(a, b));
}
long long int fact(long long int x) {
  long long int ans = 1;
  if (x == 0) {
    return 1;
  }
  while (x > 0) {
    ans = (ans * x) % 1000000007;
    x--;
  }
  return ans % 1000000007;
}
long long int power(long long int a, long long int b) {
  long long int ans = 1;
  while (b > 0) {
    if (b % 2 == 1) {
      ans *= a;
      ans = ans;
    }
    b /= 2;
    a *= a;
    a = a;
  }
  return ans;
}
vector<long long int> getbinary(int x) {
  vector<long long int> bin(10, 0);
  long long int iter = 0;
  while (x > 0) {
    if (x % 2 == 1) {
      bin[iter] = 1;
    } else {
      bin[iter] = 0;
    }
    iter++;
    x /= 2;
  }
  return bin;
}
int main() {
  string s1, s2;
  cin >> s1 >> s2;
  vector<long long int> a[26];
  long long int n = s1.length(), i, x = -1, s = 1;
  for (i = 0; i < n; i++) {
    a[s1[i] - 'a'].push_back(i);
  }
  n = s2.length();
  for (i = 0; i < n; i++) {
    if (a[s2[i] - 'a'].size() == 0) {
      cout << -1;
      return 0;
    }
    long long int y = x;
    x = upper_bound(a[s2[i] - 'a'].begin(), a[s2[i] - 'a'].end(), y) -
        a[s2[i] - 'a'].begin();
    if (x == a[s2[i] - 'a'].size()) {
      x = a[s2[i] - 'a'][0];
      s++;
    } else {
      x = a[s2[i] - 'a']
           [upper_bound(a[s2[i] - 'a'].begin(), a[s2[i] - 'a'].end(), y) -
            a[s2[i] - 'a'].begin()];
    }
  }
  cout << s << endl;
}
