Question about molecular structure (chemistry related)

My professor wants the class to put some different chemical formulas in molecular structure while following the HONC Rule. He gave us six different chemical forumals to convert and I have finished five of them correctly; however, there is still one giving me trouble. Here is the given formula: $$C^{4}H^{13}NO^{3}$$

Now, I've worked on this problem for about 30 minutes tonight. And every way I work it out I end up using 12 hydrogens, not 13. I'm beginning to think this is one of those formulas that cannot be put into molecular forum.

Any help is greatly appreciated.

EDIT: I cannot get the LaTeX to come out looking right. So I hope y'all understand that its just 4 Carbons, 13 Hydrogens, 1 Nitrogen, and 3 Oxygens. Sorry for the inconvienence.

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