Large Inside Loop of Other

Question

The challenge is to find x different ways to divide the object, for 3 people where each has to receive a value less than or equal to M, and the sum of the value that each won has to be equal to N, follows below the code that I made:

int m,n;
m = 98765;
n = 100000;

for (int i = m; i > 0; i--)
            {
                for (int j = m; j > 0; j--)
                {
                    for (int b = m; b > 0; b--)
                    {
                        Console.WriteLine(i + "   " + j + "    " + b);
                        if (i + j + b == n)
                        {
                            Console.WriteLine(somas++);
                           /* As linhas abaixo são para observar como decorre o programa */
                            Console.WriteLine(i + "   " + j + "    " + b);//
                        }
                    }

                }

            }

however, for the specified values of N and M, the project will take TOO long to give the result, there is some way, to simplify this, some theorem, or something like that, something that would make it go faster. Thank you