Error in output in following code

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C#

class Program
{

static void Main(string[] args)
{
List<string> list = new List<string>();
list.Add("Amit");
list.Add("Raj");
list.Add("prem");
list.Add("Ram");
list.Add("pa");
foreach (string s in list)
{
Console.WriteLine(s);
}
Console.WriteLine(list.Capacity);
Console.WriteLine("Enter the name which you want to search: \t");
string a = Convert.ToString(Console.ReadLine());
int b = list.BinarySearch(a);
Console.WriteLine(b);
if (b >= 0)
{
Console.WriteLine("List is contains the Name");

}
else
{
Console.WriteLine("List is NOT contains the Name");
}

Console.ReadLine();
}
}

shows output:
Amit
Raj
Prem
Ram
pa
8
Enter the name which you want to search:
pa
-2
List is NOT contain the name



Please suggest some thing about this erro because that string is already in the list
explain the error.....Please