N = int(input())

dp = [[0]*2 for n in range(N + 1)]

pre_x = 0
pre_y = 0

for n in range(1, N + 1):
    x, y = map(int, input().split())
    aa = 0
    ab = 0
    ba = 0
    bb = 0
    if x == y:
        aa = ab = ba = bb = x
    
    if pre_y == x:
        aa += x
    
    if pre_y == y:
        ab += y

    if pre_x == x:
        ba += x
    
    if pre_x == y:
        bb += y
    
    pre_x = x
    pre_y = y

    dp[n][0] = max(dp[n][0], dp[n - 1][0] + aa, dp[n - 1][1] + ba)
    dp[n][1] = max(dp[n][1], dp[n - 1][0] + ab, dp[n - 1][1] + bb)

print(max(dp[N]))