using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices.ComTypes;

namespace AtCoder.Contest.E
{
	static class Program
	{
		public static void Main(string[] args)
		{
			var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
			Console.SetOut(sw);

            Console.WriteLine(Solve());

			Console.Out.Flush();
		}

		public static long Solve()
        {
			var cin = new Scanner();

			string s = cin.Next();
			int n = s.Length;
			string t = cin.Next();
			int m = t.Length;
			long ans = -1;
			var l = new List<List<long>>();
            for (int i = 0; i < 26; i++)
            {
				l.Add(new List<long>());
            }
            for (int i = 0; i < n; i++)
            {
				l[s[i] - 'a'].Add(i);
            }
			if (n == 1)
			{
				for (int j = 0; j < m; j++)
				{
					if (s[0] != t[j]) return -1;
				}
				return m;
			}
			else
			{
				for (int i = 0; i < m; i++)
				{
					int next = t[i] - 'a';
					var e = l[next].LowerBound(ans % n + 1);
					if (e >= l[next].Count)
					{
						ans = (ans + n) / n * n;
						e = l[next].LowerBound(ans % n);
						if (e >= l[next].Count) return -1;
					}
					ans = ans / n * n;
					ans += l[next][e];
				}
				return ans + 1;
			}
        }
	}

	static class BinarySearch
	{
		public static int UpperBound<T>(T[] array, T value) => UpperBound(array, 0, array.Length - 1, value, Comparer<T>.Default);

		public static int UpperBound<T>(T[] array, T value, Comparer<T> comparer) => UpperBound(array, 0, array.Length - 1, value, comparer);

		public static int UpperBound<T>(T[] array, int index, int length, T value) => UpperBound(array, index, length, value, Comparer<T>.Default);

		public static int UpperBound<T>(T[] array, int index, int length, T value, Comparer<T> comparer)
		{
			var l = index;
			var r = l + length - 1;
			while (l <= r)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(array[mid], value);
				if (res <= 0) l = mid + 1;
				else r = mid - 1;
			}
			return l;
		}

		public static int UpperBound<T>(this List<T> list, T item) => list.UpperBound(0, list.Count, item, Comparer<T>.Default);

		public static int UpperBound<T>(this List<T> list, T item, Comparer<T> comparer) => list.UpperBound(0, list.Count, item, comparer);

		public static int UpperBound<T>(this List<T> list, int index, int count, T item, Comparer<T> comparer)
		{
			var l = index;
			var r = l + count - 1;
			while (l <= r)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(list[mid], item);
				if (res <= 0) l = mid + 1;
				else r = mid - 1;
			}
			return l;
		}

		public static int LowerBound<T>(T[] array, T value) => LowerBound(array, 0, array.Length - 1, value, Comparer<T>.Default);

		public static int LowerBound<T>(T[] array, T value, Comparer<T> comparer) => LowerBound(array, 0, array.Length - 1, value, comparer);

		public static int LowerBound<T>(T[] array, int index, int length, T value) => LowerBound(array, index, length, value, Comparer<T>.Default);

		public static int LowerBound<T>(T[] array, int index, int length, T value, Comparer<T> comparer)
		{
			var l = index;
			var r = l + length - 1;
			while (l <= r)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(array[mid], value);
				if (res == -1) l = mid + 1;
				else r = mid - 1;
			}
			return l;
		}

		public static int LowerBound<T>(this List<T> list, T item) => list.LowerBound(0, list.Count, item, Comparer<T>.Default);

		public static int LowerBound<T>(this List<T> list, T item, Comparer<T> comparer) => list.LowerBound(0, list.Count, item, comparer);

		public static int LowerBound<T>(this List<T> list, int index, int count, T item, Comparer<T> comparer)
		{
			var l = index;
			var r = l + count - 1;
			while (l <= r)
			{
				var mid = l + (r - l) / 2;
				var res = comparer.Compare(list[mid], item);
				if (res == -1) l = mid + 1;
				else r = mid - 1;
			}
			return l;
		}
	}

	class Scanner
	{
		string[] s;
		int i;

		char[] cs = new char[] { ' ' };

		public Scanner()
		{
			s = new string[0];
			i = 0;
		}

		public string Next()
		{
			if (i < s.Length) return s[i++];
			string st = Console.ReadLine();
			while (st == "") st = Console.ReadLine();
			s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
			if (s.Length == 0) return Next();
			i = 0;
			return s[i++];
		}

		public int NextInt()
		{
			return int.Parse(Next());
		}

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = NextInt() + add;
			}
			return Array;
		}

		public long NextLong()
		{
			return long.Parse(Next());
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = NextLong() + add;
			}
			return Array;
		}

		public double NextDouble()
		{
			return double.Parse(Next());
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++)
			{
				Array[i] = NextDouble() + add;
			}
			return Array;
		}
	}
}

Measured memory_bytes: 16864