Most frequent number in Array

//Find the most frequent number in the array:

Console.WriteLine("Enter length of the array: ");
int length;

//Length must be non-negative integer.
do
{
    Console.Write("Length = ");
}
while(!int.TryParse(Console.ReadLine(), out length) || length < 0);

int[] array = new int[length];

for(int i = 0; i < length; i++)
{
    array[i] = Console.ReadLine();
}

int mostFrequent = 0;
int maxCount = 0;

for(int i = 0; i < array.Length; i++)
{
  int counter = 0;// declaring the temp counter which will count the current occurrences of the number.

  for(int j = 0; j < array.Length; j++)
  {
      if(array[j] == array[i])
      {
          counter++;
      }
  }
  if(counter > maxCount)
  {
      maxCount = counter;
      mostFrequent = array[i];
  }
}
Console.WriteLine("Most frequent number in array: {0}\nRepeated {1}", mostFrequent, maxCount);