Why is the 2nd Chiral Carbon of Cephalexin R?

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The second chiral carbon of cephalexin is designated as R due to the priority of the substituents attached to it. The nitrogen (N) and sulfur (S) atoms have higher atomic weights than oxygen (O), which influences their priority ranking. The carbon bonded to N and S is assigned second priority, while the hydrogen (H) is considered fourth. This prioritization leads to the conclusion that the configuration is R rather than S. Understanding these priority rules is crucial for determining the stereochemistry of chiral molecules like cephalexin.
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Why is the 2nd chiral carbon of cephalexin molecule R? I thought the N has first priority, then the Carbon with the double bond to the O would be second (b/c has no H), and the Carbon bonded to the S would be third priority b/c it has a hydrogen, and of course, H is fourth... But then it would be S if that was the case... Why is it R?
 
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Never mind. Well, not that anyone was going to answer anyway.

But the chiral carbon in question is bonded to an S and an N. S and N have a greater atomic weight than O. So the H doesn't matter.

The Carbon bonded to the S and N is second priority.
 
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