N = int(input())
PA = [tuple(map(int, input().split())) for _ in range(N)]
dp = [[0] * (2) for _ in range(N + 1)]
dp[0][1] = -10**10

for i in range(1, N + 1):
    for j in range(2):
        dp[i][j] = max(dp[i - 1][0] + PA[i - 1][j],
                       dp[i - 1][1] + 2*PA[i - 1][j])

ans = dp[-1][0]
print(ans)