First write it out in normal type language, and convert the result to C#. Something like:
Let number1 = 0
Let number2 = 1
Print "0"
Print "1"
Let limit = << input from user
While limit > 0
Do
Let sum = number1 + number2
Print sum
Let number1 = number2
Let number2 = sum
Let limit = limit - 1
Done