using System;
class Program {
static void Main() {
Console.Write("n: ");
var n = int.Parse(Console.ReadLine());
Console.Write("x: ");
var x = double.Parse(Console.ReadLine());
var sum = 0.0;
for (var k = 0; k <= n; ++k) {
var next = Math.Pow(x, k) / ((k + 1) * (k + 3));
sum += k % 2 != 0 ? -next : next;
}
Console.WriteLine($"sum: {sum}");
Console.ReadKey();
}
}