using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] nums = Console.ReadLine().Split(' ');
           long n = int.Parse(nums[0]);
           long m = int.Parse(nums[1]);
            if (0 <= n && n <= 40000)
            {
                if (0 <= m && m <= 40000)
                {
                    Console.WriteLine(n * (m + 1));
                    Console.ReadKey();
                }
            }
        }
    }
}

I suggest you to remove "if" statements, because there is no alternative output provided.
Also, try to remove Console.ReadKey(); line before posting your code.