using System;

public class Hello
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        var b = new int[n];
        for (int i = 0; i < n; i++)
            b[i] = a[2 * i] - a[2 * i + 1];
        Console.WriteLine(getAns(n, b));
    }
    static long getAns(int n, int[] a)
    {
        var ans = 0L;
        var L = 0;
        var r = n - 1;
        for (int i = 0; i < n; i++)
        {
            if (a[L] >= -a[r]) { ans += a[L]; L++; }
            else { ans += -a[r]; r--; }
        }
        return ans;
    }
}