n = int(input())
p, a = map(int, input().split())
pp = p
aa = a
for _ in range(n - 1):
    p, a = map(int, input().split())
    p_tmp = max(pp + p, aa + p * 2)
    a_tmp = max(pp + a, aa + a * 2)
    pp = p_tmp
    aa = a_tmp
print(max(pp, aa))