Consider the following molecules: $\mathrm{Br}_3 \mathrm{O}_8, \mathrm{~F}_2 \mathrm{O}, \mathrm{H}_2 \mathrm{~S}_4 \mathrm{O}_6, \mathrm{H}_2 \mathrm{~S}_5 \mathrm{O}_6$, and $\mathrm{C}_3 \mathrm{O}_2$. Count the number of atoms existing in their zero oxidation state in each molecule. Their sum is $\_\_\_\_$ .