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 Rust (1.15.1) (judge verdict: Wrong Answer)

use std::io::prelude::*;

fn input<T: std::str::FromStr>() -> T {
    let stdin = std::io::stdin();
    let token: String = stdin
        .lock()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}

#[allow(dead_code)]
fn with_stdout_lock<F: FnOnce(std::io::BufWriter<std::io::StdoutLock>)>(f: F) {
    let out = std::io::stdout();
    let w = std::io::BufWriter::new(out.lock());
    f(w);
}

#[allow(unused_macros)]
macro_rules! debug {
    ($var:expr) => {
        match &$var { v => eprintln!(concat!(stringify!($var), "={:?}"), v) }
    };
    ($var:expr, $($vars:expr),*) => {
        match &$var { v => eprint!(concat!(stringify!($var), "={:?} "), v) }
        debug!($($vars),*);
    };
}

fn main() {
    let s: Vec<char> = input::<String>().chars().collect();
    let t: Vec<char> = input::<String>().chars().collect();

    let mut tbl = vec![vec![]; 26];
    for i in 0..s.len() {
        let c = s[i] as u8 - b'a';
        tbl[c as usize].push(i);
    }

    let mut ans = 1;
    let mut i = 0;
    let mut ok = true;
    for j in 0..t.len() {
        let c = t[j] as u8 - b'a';
        if tbl[c as usize].is_empty() {
            ok = false;
            break;
        }
        let k = tbl[c as usize].lower_bound(&i);
        if k == tbl[c as usize].len() {
            let rem = s.len() - i;
            i = tbl[c as usize][0];
            ans += (rem + i) as i64;
        } else {
            ans += (tbl[c as usize][k] - i) as i64;
            i = tbl[c as usize][k];
        }
    }

    if !ok {
        println!("-1");
    } else {
        println!("{}", ans);
    }
}

trait LowerBound<T: Ord> {
    fn lower_bound_by<F: FnMut(&T) -> std::cmp::Ordering>(&self, f: F) -> usize;
    fn lower_bound(&self, x: &T) -> usize {
        self.lower_bound_by(|e| e.cmp(x))
    }
    fn lower_bound_by_key<U: Ord, F: FnMut(&T) -> U>(&self, x: &U, mut f: F) -> usize {
        self.lower_bound_by(|e| f(e).cmp(x))
    }
}
impl<T: Ord> LowerBound<T> for [T] {
    fn lower_bound_by<F: FnMut(&T) -> std::cmp::Ordering>(&self, mut f: F) -> usize {
        let mut l = -1 as i64;
        let mut r = self.len() as i64;
        while r - l > 1 {
            let m = ((l + r) / 2) as usize;
            if f(&self[m]) == std::cmp::Ordering::Less {
                l = m as i64;
            } else {
                r = m as i64;
            }
        }
        r as usize
    }
}