N = int(input())
xy = []
offset = 0
for _ in range(N):
    x, y = map(int, input().split())
    xy.append((x, y))
    offset += (x == y) * y


dp = [0] * 2
for i in range(1, N):
    ndp = [0] * 2

    ndp[1] = max(ndp[1], dp[0] + (xy[i - 1][0] == xy[i][0]) * xy[i][0])
    ndp[1] = max(ndp[1], dp[1] + (xy[i - 1][1] == xy[i][0]) * xy[i][0])

    ndp[0] = max(ndp[0], dp[0] + (xy[i - 1][0] == xy[i][1]) * xy[i][1])
    ndp[0] = max(ndp[0], dp[1] + (xy[i - 1][1] == xy[i][1]) * xy[i][1])

    dp = ndp[:]

    # print(i, dp)

print(max(dp) + offset)