n = int(input())
pa = [list(map(int, input().split())) for i in range(n)]
pa.append([0, 0])
dp = [[0] * 2 for i in range(n + 1)]
for i in range(1, n + 1):
    dp[i][0] = pa[i - 1][0] + max(dp[i - 1][0], dp[i - 1][1])
    dp[i][1] = pa[i - 1][1] + max(dp[i - 1][0] + pa[i][0], dp[i - 1][1] + pa[i][1])
print(dp[-1][0])