using System;
using System.Collections.Generic;
using System.Linq;
using static Input;

public class Prog
{
    public struct Pair { public int x, y; public Pair(int x, int y) { this.x = x; this.y = y; } }
    public static void Solve()
    {
        string s = NextString();
        string t = NextString();
        if (s == t) { Console.WriteLine(s.Length); return; }
        Dictionary<char, List<int>> d = new Dictionary<char, List<int>>();
        for (char c = 'a'; c <= 'z'; c++) d[c] = new List<int>();
        for (int i = 0; i < s.Length; i++) { d[s[i]].Add(i); }

        int now_ind = -1;
        long ans = 0;
        for (int i = 0; i < t.Length; i++)
        {
            //t[i]があるか探す
            if (d[t[i]].Count() == 0) { ans = -1; break; }
            else
            {
                if (1 <= i && t[i - 1] == t[i] && d[t[i]].Count() == 1)
                {
                    ans++;
                    //Console.WriteLine("=" + now_ind.ToString());
                }
                else if (now_ind < d[t[i]].First())
                {
                    //周期変更なし
                    now_ind = d[t[i]].First();
                    //Console.WriteLine("<" + now_ind.ToString());
                }
                else if (d[t[i]].Last() < now_ind + 1)
                {
                    //必ず周期変更する
                    ans++;
                    now_ind = d[t[i]].First();
                    //Console.WriteLine(">" + now_ind.ToString());
                }
                else
                {
                    //二部探索で超える場所を探す
                    now_ind = d[t[i]][UpperBound(d[t[i]], now_ind)];
                    //Console.WriteLine("0" + now_ind.ToString());
                }
            }
        }
        if (ans == -1) Console.WriteLine(-1);
        else Console.WriteLine(ans * (long)(s.Length) + now_ind + 1);
    }
    private static int UpperBound(List<int> list, int n)
    {
        int a = 0, b = list.Count();
        while (b - a != 1)
        {
            int x = (a + b) / 2;
            if (list[x] > n) b = x;
            else a = x;
        }
        return b;
    }
    private static int LowerBound(List<int> list, int n)
    {
        int a = 0, b = list.Count();
        if (list[b - 1] <= n) return b - 1;
        else if (list[a] > n) return -1;
        while (b - a != 1)
        {
            int x = (a + b) / 2;
            if (list[x] <= n) a = x;
            else b = x;
        }
        return a;
    }
    public static void Main()
    {
        var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        Solve();
        Console.Out.Flush();
    }
}
public class Input
{
    public const long MOD = 1000000007;
    public const int INF = 1000000007;
    private static Queue<string> q = new Queue<string>();
    private static void Confirm() { if (q.Count == 0) foreach (var s in Console.ReadLine().Split(' ')) q.Enqueue(s); }
    public static int NextInt() { Confirm(); return int.Parse(q.Dequeue()); }
    public static long NextLong() { Confirm(); return long.Parse(q.Dequeue()); }
    public static string NextString() { Confirm(); return q.Dequeue(); }
    public static double NextDouble() { Confirm(); return double.Parse(q.Dequeue()); }
    public static int[] LineInt() { return Console.ReadLine().Split(' ').Select(int.Parse).ToArray(); }
    public static long[] LineLong() { return Console.ReadLine().Split(' ').Select(long.Parse).ToArray(); }
    public static string[] LineString() { return Console.ReadLine().Split(' ').ToArray(); }
    public static double[] LineDouble() { return Console.ReadLine().Split(' ').Select(double.Parse).ToArray(); }
}


Measured memory_bytes: 16096