package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
	return scanner
}
func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextUint64(scanner *bufio.Scanner) uint64 {
	i, _ := strconv.ParseUint(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	cnt := 0
	if os.Getenv("MASPY") == "ますピ" {
		fp, _ = os.Open(os.Getenv("BEET_THE_HARMONY_OF_PERFECT"))
		cnt = 2
	}
	if os.Getenv("MASPYPY") == "ますピッピ" {
		wfp, _ = os.Create(os.Getenv("NGTKANA_IS_GENIUS10"))
	}
	scanner := getScanner(fp)
	writer := bufio.NewWriter(wfp)
	solve(scanner, writer)
	for i := 0; i < cnt; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
	writer.Flush()
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner) << 1
	aa := makeGrid(2, n)
	for i := 0; i < n; i++ {
		aa[i%2][i] = getNextInt64(scanner)
	}
	for i := 0; i < n-1; i++ {
		for j := 0; j < 2; j++ {
			aa[j][i+1] += aa[j][i]
		}
	}
	var ans int64
	for i := 0; i < n; i += 2 {
		ans = maxint(ans, before(i, aa[0])+after(i, aa[1])-(before(i, aa[1])+after(i, aa[0])))
	}
	fmt.Fprintln(writer, ans)
}
func maxint(a, b int64) int64 {
	if a < b {
		return b
	}
	return a
}
func before(i int, aa []int64) int64 {
	if i == 0 {
		return 0
	}
	return aa[i-1]
}

func after(i int, aa []int64) int64 {
	if i == 0 {
		return aa[len(aa)-1]
	}
	return aa[len(aa)-1] - aa[i-1]
}

func makeGrid(h, w int) [][]int64 {
	index := make([][]int64, h, h)
	data := make([]int64, h*w, h*w)
	for i := 0; i < h; i++ {
		index[i] = data[i*w : (i+1)*w]
	}
	return index
}