import sys
sys.setrecursionlimit(10**7)
def ii(): return int(input())
def mi(d=0): return map(lambda x:int(x)-d,input().split())
INF = float("inf")
MOD = 998244353
def answer(s):
  print(s)
  exit()
def cross(xy):
  x,y = xy
  return (x+1,y),(x-1,y),(x,y+1),(x,y-1)
################################################
n = ii()
back = [-1,-1]
score = [0,0]
for _ in range(n):
  x,y = mi()
  nb = [-1,-1]
  ns = [0,0]
  if x == y:
    ns[0] += x
    ns[1] += x
  i = 0
  for x,y in ((x,y),(y,x)):
    if x in back:
      ns[i] = max(score[back.index(x)] + x,max(score))
    else:
      ns[i] = max(score)
    nb[i] = y
    i += 1
  back = nb
  score = ns
print(max(score))