package main

import (
  "bufio"
  "fmt"
  "os"
  "strconv"
  "sort"
  "strings"
  _ "math"
)

func main() {
  scanner := bufio.NewScanner(os.Stdin)
  hold := []int{}
  edit_raw := make(map[int]string)
  for scanner.Scan() {
    for _, num_s := range strings.Split(scanner.Text(), " ") {
      runes := []rune(num_s)
      for i, r := range runes{
        if r == []rune("4")[0] {
          runes[i] = []rune("7")[0]
        }else if r == []rune("7")[0] {
          runes[i] = []rune("4")[0]
        }
      }
      num, _ := strconv.Atoi(string(runes))
      edit_raw[num] = num_s
      hold = append(hold, num)
    }
    break
  }
  nums := hold
  sort.Ints(nums)
  _, tail := nums[0], nums[1]
  
  fmt.Println(edit_raw[tail])
}