Fibonacci in MARIE Simulator

[honberiz]

I'm writing a program for class, to calculate the Fibonacci number given the n value. For some reason, my output goes negative at N=24. Does anyone understand MARIE Simulator enough to figure out what the issue is?

ORG	100
	Input	Input number
	Store	N
	Store	Ctr

Loop1,	Clear
	Load Ctr
	Subt C1
	Store Ctr
	Load F2
	Add F1
	Store F3
	Load F1
	Store F2
	Load F3
	Store F1
	Load Ctr
	Skipcond 400
	Jump Loop1

	Load Ctr
	Output

	Load N
	Output

	Load F1
	Output

	Halt 

	N, DEC 0 
	Ctr, DEC 0 
	C1, DEC 1
	F1, DEC 0
	F2, DEC 1
	F3, DEC 0

Thanks