#nullable enable

var n = int.Parse(Console.ReadLine()!);
var last = ((0L, 0), (0L, 0));
for (var i = 0; i < n; i++)
{
    var input = Console.ReadLine()!.Split(' ');
    var x = int.Parse(input[0]);
    var y = int.Parse(input[1]);
    var d = x == y ? x : 0;
    var ((s1, l1), (s2, l2)) = last;
    var xns1 = s1 + d + (l1 == y ? y : 0);
    var xns2 = s2 + d + (l2 == y ? y : 0);
    var xns = Math.Max(xns1, xns2);
    var yns1 = s1 + d + (l1 == x ? x : 0);
    var yns2 = s2 + d + (l2 == x ? x : 0);
    var yns = Math.Max(yns1, yns2);
    last = ((xns, x), (yns, y));
}
Console.WriteLine(Math.Max(last.Item1.Item1, last.Item2.Item1));