N=int(input())
ans=0
p=[0]*(N+1)
a=[0]*(N+1)
dp1=[0]*(N+1)
dp2=[0]*(N+1)
for i in range(N):
    p[i],a[i]=map(int,input().split())
for i in range(N-1,-1,-1):
    dp1[i]=p[i]+max(dp1[i+1],dp2[i+1])
    dp2[i]=a[i]+max(dp1[i+1]+p[i+1],dp2[i+1]+a[i+1])
print(max(dp1[0],dp2[0]))