package main
import (
"bufio"
"fmt"
"os"
"strings"
)
func main() {
hash := map[string][]string{}
in := bufio.NewScanner(os.Stdin)
winner := map[rune]string{
'A': "B",
'B': "C",
'C': "A",
}
for in.Scan() {
str := in.Text()
if len(str) == 0 {
break
}
s := strings.Split(str, " ")
hash[s[1]] = append(hash[s[1]], s[0])
}
if len(hash) != 2 {
fmt.Println("NULL")
return
}
for ch := 'A'; ch <= 'C'; ch++ {
if _, ok := hash[string(ch)]; !ok {
win := winner[ch]
for _, name := range hash[win] {
fmt.Println(name)
}
return
}
}
}