package main

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

func main() {
	reader := bufio.NewReader(os.Stdin)
	var n int
	if _, err := fmt.Fscan(reader, &n); err != nil {
		return
	}

	a := make([]int, n)
	maxVal := 0
	for i := 0; i < n; i++ {
		fmt.Fscan(reader, &a[i])
		if a[i] > maxVal {
			maxVal = a[i]
		}
	}

	stack := make([]int, 0, n)
	for i := 0; i < n; i++ {
		x := a[i]
		if len(stack) == 0 {
			stack = append(stack, x)
		} else if stack[len(stack)-1] == x {
			stack = stack[:len(stack)-1]
		} else if stack[len(stack)-1] > x {
			stack = append(stack, x)
		} else {
			fmt.Println("NO")
			return
		}
	}

	if len(stack) > 1 {
		fmt.Println("NO")
	} else if len(stack) == 1 && stack[0] != maxVal {
		fmt.Println("NO")
	} else {
		fmt.Println("YES")
	}
}