## https://yukicoder.me/problems/no/3289

def main():
    N = int(input())
    xy = []
    for _ in range(N):
        x, y = map(int, input().split())
        xy.append((x, y))

    
    dp = [0, 0]
    for i in range(N):
        new_dp = [-1, -1]

        base = 0
        if xy[i][0] == xy[i][1]:
            base += xy[i][0]

        # dp[j] = 前のとき、どう言う並びにしたか
        for j in range(2):
            for k in range(2):
                if i == 0:
                    new_dp[k] = max(new_dp[k], dp[j] + base)
                else:
                    if xy[i - 1][1 - j] == xy[i][k]:
                        x =xy[i][k]
                        new_dp[k] = max(new_dp[k], dp[j] + x + base)
                    else:
                        new_dp[k] = max(new_dp[k], dp[j] + base)
        dp = new_dp
    answer = max(dp)
    print(answer)



if __name__ == "__main__":
    main()