N=int(input())
P=[0]*(N+1)
A=[0]*(N+1)

for i in range(1,N+1):
    p,a=map(int,input().split())
    P[i]=p
    A[i]=a

S=[[0,0] for _ in range(N+1)]

S[-1][0]=P[-1]
S[-1][1]=A[-1]

for i in range(N-1,-1,-1):
    S[i][0]=max(S[i+1][0],S[i+1][1])+P[i]
    S[i][1]=max(S[i+1][0]+P[i+1],S[i+1][1]+A[i+1])+A[i]
print(S[0][0])