using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    static string[] SList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => ReadLine()).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var map = NArr(n);
        var dp = new long[2];
        for (var i = 0; i < n; ++i)
        {
            if (i == 0)
            {
                dp[0] = map[0][0] == map[0][1] ? map[0][0] : 0;
                dp[1] = dp[0];
            }
            else
            {
                var ndp = new long[2];
                ndp[0] = Math.Max(dp[0] + (map[i - 1][1] == map[i][0] ? map[i][0] : 0), dp[1] + (map[i - 1][0] == map[i][0] ? map[i][0] : 0));
                ndp[1] = Math.Max(dp[0] + (map[i - 1][1] == map[i][1] ? map[i][1] : 0), dp[1] + (map[i - 1][0] == map[i][1] ? map[i][1] : 0));
                if (map[i][0] == map[i][1])
                {
                    ndp[0] += map[i][0];
                    ndp[1] += map[i][1];
                }
                dp = ndp;
            }
        }
        WriteLine(Math.Max(dp[0], dp[1]));
    }
}