package main

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

func main() {
	rd:=bf.NewReader(Stdin)
	var n int
	Fscan(rd,&n)
	yxsum, xysum := 0,0
	yxlast, xylast := 0, 0
	for i := 0; i < n; i++ {
		var x, y int
		Fscan(rd,&x,&y)
		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
	}
	Println(max(yxsum,xysum))
}

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