import sys
input = sys.stdin.readline

from collections import Counter

n=int(input())
DP=Counter()

DP[-1]=0

for i in range(n):
    x,y=map(int,input().split())

    NDP=Counter()

    if x==y:
        for dp in DP:
            score=DP[dp]
            if dp==x:
                score+=x
            score+=x

            NDP[x]=score
    else:
        for dp in DP:
            score=DP[dp]

            if x==dp:
                score+=x

            NDP[y]=max(NDP[y],score)

            score=DP[dp]

            if y==dp:
                score+=y
            NDP[x]=max(NDP[x],score)

    DP=NDP

ANS=max(DP.values())

print(ANS)