How many nitrogen atoms are in a 2.51 mol sample of N_2O?

$5.02 \times {N}_{A}$, where ${N}_{A} = \text{Avogadro's number}$
${N}_{A} = 6.022 \times {10}^{23} \cdot m o {l}^{-} 1$
Clearly there are $5.02 \times {N}_{A}$ nitrogen atoms in a $2.51 \cdot m o l$ sample. How many oxygen atoms?