n=int(input())
p1,p2=map(int,input().split())
q=[(p2==p1)*p2,(p1==p2)*p1]
for _ in range(1,n):
  nq=[0,0]
  p3,p4=map(int,input().split())
  nq[0]=max(q[0]+(p1==p4)*p1+(p3==p4)*p3,q[1]+(p2==p4)*p2+(p3==p4)*p3)
  nq[1]=max(q[0]+(p1==p3)*p1+(p3==p4)*p3,q[1]+(p2==p3)*p2+(p3==p4)*p3)
  q=nq
  p1,p2=p3,p4
print(max(q))