N=int(input())
dp=[[0]*2 for i in range(N+1)]
a,b=-1,-1
for i in range(N):
  x,y=map(int,input().split())
  v=[a,b]
  h=[x,y]
  for j in range(2):
    for k in range(2):
      d=dp[i][j]
      if v[j]==h[k]:
        d+=v[j]
      if x==y:
        d+=x
      dp[i+1][k]=max(dp[i+1][k],d)
  a,b=y,x
print(max(dp[N]))