package main

import . "fmt"
import . "os"
import bf "bufio"

func main() {
	rd:=bf.NewReader(Stdin)
	var n int
	Fscan(rd,&n)
	xs := make([]int, n)
	ys := make([]int, n)
	for i:=0; i< n; i++ {
		Fscan(rd,&xs[i],&ys[i])
	}
	ans := solve2(n, xs, ys)
	Println(ans)
}

func solve(n int, xs, ys []int) int {
	yxsum, xysum := 0,0
	yxlast, xylast := 0, 0
	for i := 0; i < n; i++ {
		x, y := xs[i], ys[i]
		yxsum += f(x, y)
		xysum += f(x, y)
		yxsum, xysum = max(yxsum+f(yxlast, y), xysum+f(xylast,y)), max(yxsum+f(yxlast,x),xysum+f(xylast,x))
		yxlast,xylast = x,y
	}
	return max(yxsum,xysum)
}

func f(a, b int) int {
	if a == b {
		return a
	} else {
		return 0
	}
}

func solve2(n int, xs, ys []int) int {
	ps := make([]int, 0, n*2)
	for i := 0; i < n; i++ {
		ps = append(ps, xs[i], ys[i])
	}
	g := func(i, j int) int {
		return f(ps[i], ps[j])
	}
	swap := func(i, j int) {
		ps[i],ps[j]=ps[j],ps[i]
	}
	ans := 0
	for k := 0; k < 3; k++ {
		for i := 1; i+1 < n; i++ {
			a,b,c,d := i*2-1,i*2,i*2+1,i*2+2
			if g(a,b)+g(c,d)<g(a,c)+g(b,d) {
				swap(b,c)
			}
		}
		for i,j := 0, len(ps)-1; i < j; i,j =i+1,j-1 {
			swap(i,j)
		}
		for i := 1; i+1 < n; i++ {
			a,b,c,d := i*2-1,i*2,i*2+1,i*2+2
			if g(a,b)+g(c,d)<g(a,c)+g(b,d) {
				swap(b,c)
			}
		}
		sum := 0
		for i := 1; i <len(ps); i++ {
			sum += g(i-1,i)
		}
		ans = max(ans, sum)
		swap(0, 1)
	}
	return ans
}