import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
# md = 998244353
md = 10**9+7

n = II()

def chmax(j, val):
    if val > ndp[j]: ndp[j] = val

dp = [0, -inf]
for i in range(n):
    p, a = LI()
    ndp = [-inf, -inf]
    for j in range(2):
        pre = dp[j]
        if j:
            chmax(0, pre+p*2)
            chmax(1, pre+a*2)
        else:
            chmax(0, pre+p)
            chmax(1, pre+a)
    dp = ndp
    # print(dp)

print(max(dp))