package main

import . "fmt"

func main() {
	var n int
	Scan(&n)
	m := map[string]int{}
	st := []string{}
	for ; n > 0; n-- {
		var s, t string
		Scan(&s,&t)
		m[s]++
		m[t]++
		st = append(st, s, t)
	}
	for i := range st {
		if i % 2 == 1 {
			continue
		}
		if m[st[i]] > 1 && m[st[i+1]] > 1 {
			Println("No")
			return
		}
	}
	Println("Yes")
}