Problem:
Score : 300 points

Problem Statement

Snuke can change a string t of length N into a string t' of length N - 1 under the following rule:

For each i (1 ≤ i ≤ N - 1), the i-th character of t' must be either the i-th or (i + 1)-th character of t.

There is a string s consisting of lowercase English letters.
Snuke's objective is to apply the above operation to s repeatedly so that all the characters in s are the same.
Find the minimum necessary number of operations.

Constraints

1 ≤ |s| ≤ 100

s consists of lowercase English letters.

Input

Input is given from Standard Input in the following format:

s

Output

Print the minimum necessary number of operations to achieve the objective.

Sample Input 1

serval

Sample Output 1

3

One solution is: serval → srvvl → svvv → vvv.

Sample Input 2

jackal

Sample Output 2

2

One solution is: jackal → aacaa → aaaa.

Sample Input 3

zzz

Sample Output 3

0

All the characters in s are the same from the beginning.

Sample Input 4

whbrjpjyhsrywlqjxdbrbaomnw

Sample Output 4

8

In 8 operations, he can change s to rrrrrrrrrrrrrrrrrr.

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::Read;
use std::collections::HashSet;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();

    let answer = solve(&buf);

    println!("{}", answer);
}

fn solve(input: &str) -> String {
    let mut iterator = input.split_whitespace();

    let s = iterator.next().unwrap();

    let mut set_list: Vec<HashSet<char>> = vec![HashSet::new(); s.len()];
    for (i, c) in s.chars().enumerate() {
        set_list[i].insert(c);
    }

    let mut done = false;
    let mut count = 0;
    while !done {
        for c in 'a' as u8..'z' as u8 + 1 {
            let c = c as char;
            if set_list.iter().all(|set| set.contains(&c)) {
                done = true;
                break;
            }
        }
        if !done {
            for i in 0..(set_list.len() - 1) {
                let next = set_list[i + 1].clone();
                set_list[i].extend(next);
            }
            set_list.pop();
            count += 1;
        }
    }

    return count.to_string();
}