How to draw a triangle from the number of characters entered by the user?

I'm trying to make a console application on .Net 6 (C#), I need the triangle to be built from the number of characters entered by the user, and not the number of LINES entered by the user.

I tried to implement a simple rendering of a triangle by timing through a nested for() loop, but my pyramid is drawn not from 6 characters, but more, from 10. I tried to implement the loop in different ways, create a new variable or add another while loop as a constant, but nothing worked.

I attached an example code below:

static void Main()
{
    Console.WriteLine("Enter the number of symbols to build pyramid: ");

    int p = Convert.ToInt32(Console.ReadLine());

    for (int i = 0; i < p; i++)
    {
        Console.WriteLine();

        for (int j = 0; j <= i; j++)
        {
            Console.Write("*");
        }
    }
}

Let's start from the math: let's find when we can draw a triangle of m lines:

(1)     *
(2)     **
(3)     ***
...     ...
(m - 1) *** ... *
(m)     *** ... ** 

So the total number of points (n)

1 + 2 + 3 + ... + m = m * (m + 1) / 2 = n

If we solve it for m we will get

m^2 + m - 2 * n = 0

m = (-1 + sqrt(1 + 8 * n)) / 2

So we can solve for m and if an integer solution exists, draw the triangle

private static bool DrawTriangle(int n) {
  if (n <= 0)
    return false;

  // we want integer solution (rounded), not a floating point one
  long m = (long)((-1.0 + Math.Sqrt(1.0 + 8.0 * n)) / 2.0);
		
  long residue = n - m * (m + 1) / 2;

  for (int i = 1; i <= m; ++i)
    Console.WriteLine(new string('*', i));
		
  if (residue > 0)
    Console.WriteLine(new string('*', (int)residue));

  return true;
}

usage:

static void Main() {
  Console.WriteLine("Enter the number of symbols to build pyramid: ");

  // TODO: int.TryParse is a better technique
  int p = Convert.ToInt32(Console.ReadLine());

  if (!DrawTriangle(p))
    Console.WriteLine("Not a positive number");
}

Fiddle

The number that the user enters must be able to make a triangle. For
example, it is not possible for the number 5:

*
**
**

But if the entered number is valid, you can use the following code:

    Console.WriteLine("Enter the number of symbols to build pyramid: ");
    int p = Convert.ToInt32(Console.ReadLine());

    int lineSize = 1;
    for (int i = 0; i < p; i++)
    {
         for (int j = 0; j < lineSize; j++)
         {
             if(j+i<p)
                 Console.Write("*");
         }
         i = i + lineSize - 1;
         Console.WriteLine();
         lineSize++;
    }

result:

Enter the number of symbols to build pyramid:
5
*
**
**
Enter the number of symbols to build pyramid:
6
*
**
***
Enter the number of symbols to build pyramid:
10
*
**
***
****
Enter the number of symbols to build pyramid:
11
*
**
***
****
*