import sys
import os


IS_LOCAL = os.environ.get("LOCAL") == "true"


def debug(*args, sep=" ", end="\n", flush=False) -> None:
    if IS_LOCAL:
        print(*args, sep=sep, end=end, file=sys.stderr, flush=flush)


def yn(flg: bool) -> bool:
    print('Yes' if flg else 'No')
    return flg


def gcd(a, b):
    a = abs(a); b = abs(b)
    if a < b: a, b = b, a
    while b > 0:
        a, b = b, a % b
    return a


def lcm(a, b):
    return a * b // gcd(a, b)


def main():
    readline = sys.stdin.readline

    N = int(readline())
    dp, ndp = [0] * 2, [0] * 2
    pre = list(map(int, readline().split()))[::-1]
    if pre[0] == pre[1]:
        dp[0] = dp[1] = pre[0]
    for _ in range(N - 1):
        tmp = list(map(int, readline().split()))
        for i in range(2):
            ndp[i] = max(dp[j] + tmp[i] * (tmp[i] == pre[j]) for j in range(2))
            if tmp[0] == tmp[1]:
                ndp[i] += tmp[0]
        pre = tmp[::-1]
        dp = ndp[:]
        debug(dp)
    print(max(dp))


if __name__ == "__main__":
    main()