n = int(input())
pa = []
for i in range(n):
    p, a = map(int, input().split())
    pa.append([p, a])
    
dp = [[0] * 2 for _ in range(n)]
dp[0][0] = pa[-1][0]
dp[0][1] = pa[-1][1]

for i in range(1, n):
    p, a = pa[-1-i]
    x, y = pa[-i]
    dp[i][0] = max(dp[i-1][0], dp[i-1][1]) + p
    dp[i][1] = max(dp[i-1][0] + x, dp[i-1][1] + y) + a

ans = max(dp[-1])
print(ans)