=== Fibonacci Series Calculator ===

First 15 Fibonacci numbers:
F(0) = 0
F(1) = 1
F(2) = 1
F(3) = 2
F(4) = 3
F(5) = 5
F(6) = 8
F(7) = 13
F(8) = 21
F(9) = 34
F(10) = 55
F(11) = 89
F(12) = 144
F(13) = 233
F(14) = 377

Specific Fibonacci calculations:
F(10) = 55
F(20) = 6765
F(30) = 832040
F(50) = 12586269025

Large Fibonacci numbers (using BigInt):
F(100) = 354224848179261915075
F(200) = 280571172992510140037611932413038677189525
F(500) = 139423224561697880139724382870407283950070256587697307264108962948325571622863290691557658876222521294125...573418161601095394088057208208297308711232827892125077126294632295639898989358211674562701021835646220134967151881909730915777
F(1000) = 43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875...

Benchmarking Fibonacci calculations for n = 30:
Iterative: 832040 (took 125ns)
Memoized: 832040 (took 2.1µs)
Recursive: Skipped (too slow for n > 35)
BigInt: 832040 (took 8.7µs)

=== Interactive Mode ===
Enter a number to calculate its Fibonacci value (or 'quit' to exit):
Enter n: 25
F(25) = 75025

Enter n: 100
F(100) = 354224848179261915075

Enter n: 1000
F(1000) = 43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875...43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875 (209 digits)

Enter n: quit
Goodbye!