How to use left-shift assignment operator ? How does it works?

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C#3.5

I have come accross the MSDN Operator (C# Reference).
But i am not able to get the working of this. When the operator is shifting a digit to left by 4
as in this example . How it is possible that it produces output of 16000 ? Thanks.

Source : http://msdn.microsoft.com/en-us/library/ayt2kcfb(v=vs.90).aspx[^]

class MainClass9
{
static void Main()
{
int a = 1000;
a <<= 4;
Console.WriteLine(a);
}
}
/*
Output:
16000
*/