package main

import (
    "fmt"
    "strings"
)

func main() {
    var (
        b      strings.Builder
        str    string
        newStr string
    )
    fmt.Scan(&str)
    for i := len(str); i > 0; i-- {
        res := strings.IndexAny(newStr, string(str[i-1]))
        if res < 0 {
            b.WriteByte(str[i-1])
            newStr = b.String()
        }
    }
    fmt.Println(newStr)
}