Problem:
Score : 500 points

Problem Statement

Given are two strings s and t consisting of lowercase English letters. Determine if there exists an integer i satisfying the following condition, and find the minimum such i if it exists.

Let s' be the concatenation of 10^{100} copies of s. t is a subsequence of the string {s'}_1{s'}_2\ldots{s'}_i (the first i characters in s').

Notes

A subsequence of a string a is a string obtained by deleting zero or more characters from a and concatenating the remaining characters without changing the relative order. For example, the subsequences of contest include net, c, and contest.

Constraints

1 \leq |s| \leq 10^5

1 \leq |t| \leq 10^5

s and t consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

s
t

Output

If there exists an integer i satisfying the following condition, print the minimum such i; otherwise, print -1.

Sample Input 1

contest
son

Sample Output 1

10

t = son is a subsequence of the string contestcon (the first 10 characters in s' = contestcontestcontest...), so i = 10 satisfies the condition.

On the other hand, t is not a subsequence of the string contestco (the first 9 characters in s'), so i = 9 does not satisfy the condition.

Similarly, any integer less than 9 does not satisfy the condition, either. Thus, the minimum integer i satisfying the condition is 10.

Sample Input 2

contest
programming

Sample Output 2

-1

t = programming is not a substring of s' = contestcontestcontest.... Thus, there is no integer i satisfying the condition.

Sample Input 3

contest
sentence

Sample Output 3

33

Note that the answer may not fit into a 32-bit integer type, though we cannot put such a case here.

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
namespace E___Strings_of_Impurity
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(solver());
        }

        static long solver()
        {
            var s = Console.ReadLine();
            var t = Console.ReadLine();

            var alphabets = new List<int>[26];
            for (int i = 0; i < 26; i++) alphabets[i] = new List<int>();
            for (int i = 0; i < s.Length; i++) alphabets[s[i] - 'a'].Add(i + 1);

            long result = 0;
            var currentIndex = 0;
            for (int i = 0; i < t.Length; i++)
            {
                var currentChar = alphabets[t[i] - 'a'];
                if (currentChar.Count == 0) return -1;
                currentIndex = binarySearch(currentChar, currentIndex);
                if (currentIndex == -1)
                {
                    result += s.Length;
                    currentIndex = currentChar[0];
                }
            }
            return result + currentIndex;
        }
        static int binarySearch(List<int> list, int key)
        {
            int left = -1;
            int right = list.Count;

            while (right - left > 1)
            {
                int mid = left + (right - left) / 2;
                if (list[mid] >= key)
                {
                    right = mid;
                }
                else
                {
                    left = mid;
                }
            }
            if (right >= list.Count)
            {
                return -1;
            }
            else
            {
                return list[right];
            }
        }
    }
}