def accum_dp(xs: list, f, op, e, init: dict):
    dp = init.copy()
    for x in xs:
        pp = {}
        dp, pp = pp, dp
        for fm_key, fm_val in pp.items():
            for to_key, to_val in f(fm_key, fm_val, x):
                dp[to_key] = op(dp.get(to_key, e), to_val)

    return dp


def f(k, v, x):
    # k : 末尾の数値

    a, b = x
    nv = v+a if a == b else v

    # k -> a -> b
    if k == a:
        yield b, nv+k
    else:
        yield b, nv

    # k -> b -> a
    if k == b:
        yield a, nv+k
    else:
        yield a, nv


INF = 1 << 62
N = int(input())

xs = []
for _ in range(N):
    X, Y = map(int, input().split())
    xs.append((X, Y))

init = {-1: 0}
dp = accum_dp(xs, f, max, 0, init)

ans = max(dp.values())
print(ans)