n = int(input())
PA = []
for i in range(n):
    p, a = map(int, input().split())
    PA.append((p, a))

dp = [0]*2
for i, (p, a) in enumerate(PA):
    nx = [0]*2
    if i != 0:
        nx[0] = max(dp[0]+2*a, dp[1]+a)
        nx[1] = max(dp[0]+2*p, dp[1]+p)
    else:
        nx[0] = a
        nx[1] = p
    dp = nx
print(max(dp))