package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

func main() {
	parents := make(map[string]bool)
	children := make(map[string]bool)
	sc := bufio.NewScanner(os.Stdin)
	for sc.Scan() {
		s := strings.Split(sc.Text(), " -> ")
		parents[parseParent(s[0])] = true
		if len(s) > 1 {
			for _, c := range parseChildren(s[1]) {
				children[c] = true
			}
		}
	}
	//fmt.Println(parents)
	//fmt.Println(children)
	fmt.Println(uniq(parents, children))
}

func parseParent(s string) string {
	return strings.Split(s, " ")[0]
}

func parseChildren(s string) []string {
	ret := []string{}
	for _, c := range strings.Split(s, ", ") {
		ret = append(ret, c)
	}
	return ret
}

func uniq(p map[string]bool, c map[string]bool) string {
	for e := range c {
		delete(p, e)
	}
	fmt.Println(len(p))
	for e := range p {
		return e
	}
	return "not found"
}