demo

int n = int.Parse(Console.ReadLine()); // n = 3
int num = int.Parse(Console.ReadLine());

int count = 0;
bool isFinish = false;

for (int row = 1;  row <= n; row++)
{
    for (int col = 1; col <= n; col++)
    {
        Console.Write("* ");
        count++;

        if (count == num)
        {
            isFinish = true;
            break;
        }
    }
    Console.WriteLine();

    if (isFinish)
        break;
}