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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
        "bufio"
        "fmt"
        "os"
)

var sc = bufio.NewScanner(os.Stdin)

func readLine() string {
    sc.Scan()
    return sc.Text()
}

func lowerBound(a []int, x int) int {
        n := len(a)
        ok := n
        ng := -1
        for ok-ng > 1 {
                mid := (ok + ng) / 2
                if a[mid] >= x {
                        ok = mid
                } else {
                        ng = mid
                }
        }
        return ok
}

func main() {
        var s string
        var t string

        s = readLine()
        t = readLine()

        idxs := make([][]int, 256)

        for i := 0; i < len(s); i++ {
                idxs[s[i]] = append(idxs[s[i]], i)
        }

        n := int64(len(s))
        cur := int64(0)
        ng := false

        for i := 0; i < len(t); i++ {
                is := idxs[t[i]]
                if is == nil || len(is) == 0 {
                        ng = true
                        break
                }
                base := (cur / n) * n

                nidx := lowerBound(is, int(cur%n))
                if nidx == len(is) {
                        cur = base + int64(is[0]) + n + 1
                } else {
                        cur = base + int64(is[nidx]) + 1
                }
        }
        if ng {
                fmt.Println(-1)
        } else {
                fmt.Println(cur)
        }
}