n = int(input())
inf = float("INF")
dp = [[-inf, -inf] for _ in range(n)]
XY = [tuple(map(int, input().split())) for _ in range(n)]
if XY[0][0] == XY[0][1]:
    dp[0][0] = XY[0][0]
else:
    dp[0] = [0, 0]

for i in range(1, n):
    if XY[i][0] == XY[i][1]:
        dp[i][0] = max(dp[i-1]) + XY[i][0]
        for j in range(2):
            if XY[i][0] == XY[i-1][j]:
                dp[i][0] = max(dp[i][0], dp[i-1][j] + XY[i][0] + XY[i][0])
    else:
        for j in range(2):
            for k in range(2):
                dp[i][k] = max(dp[i][k], dp[i-1][0], dp[i-1][1])
                if XY[i-1][j] == XY[i][k]:
                    dp[i][k^1] = max(dp[i][k^1], dp[i-1][j] + XY[i][k])

print(max(dp[-1]))