N = int(input())
l = []
for _ in range(N):
    p,a = map(int,input().split())
    l.append((p,a))

dp = [[0] * 2 for _ in range(N)]
dp[0][0] = l[-1][0]
dp[0][1] = l[-1][1]
for i in range(1,N):
    p,a = l[-1-i]
    pp,aa = l[-i]
    dp[i][1] = max(dp[i-1][0] + pp,dp[i-1][1] + aa) + a
    dp[i][0] = max(dp[i-1][0],dp[i-1][1]) + p
print(max(dp[-1]))