N = int(input())
inf = 10 ** 18
dp = [[-inf] * 2 for i in range(N + 1)]
dp[0][0] = 0
D = []
for i in range(N):
    D.append(list(map(int, input().split())))

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