Nitrogen reactions

Question

Hello, I was going through some older chemistry olympiad tasks and I got stuck on this problem. It is basically an reaction chain and you have to complete chemical formulas into the reactions. In brackets there are either catalysts, other reactants or reaction conditions.
A--(H2O)->B--(O2, Pt, 1200K)->C--(H2, H2SO4, Pt/C)->D--(MeOH, MeONa)->E
And also you know that all the compounds contain Nitrogen and that A contains 27.8% of N.

I tried to think about all the Nitrogen compounds I know, but I wasn't succesful even with the very first reaction. Then I tried a different approach and rather than just making up compounds I know and testing this chain, I tried to count the molar weight of the first compound (since I know it contains 27.8% of N) and I got about 50.4. When I tried searching to a compound containing Nitrogen that has molar weight of 50.4 I had no luck.

Could you please advice which way to go and what compounds could that be?
Please Help.
Thanks !

I didn't find the right solution from the internet.
References:
- http://www.chemicalforums.com/index.php?topic=89449.06514651
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