03. Combinations

int n = int.Parse(Console.ReadLine());
int count = 0;

for (int x1 = 0; x1 <= n; x1++)
{
    for (int x2 = 0; x2 <= n; x2++)
    {
        for (int x3 = 0; x3 <= n; x3++)
        {
            int sum = x1 + x2 + x3;

            if (sum == n)
            {
                count++;
            }
        }
    }
}

Console.WriteLine(count);