The total number of compounds having at least one bridging oxo group among the molecules given below is ____.
$\mathrm{N}_2 \mathrm{O}_3, \mathrm{~N}_2 \mathrm{O}_5, \mathrm{P}_4 \mathrm{O}_6, \mathrm{P}_4 \mathrm{O}_7, \mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_5, \mathrm{H}_5 \mathrm{P}_3 \mathrm{O}_{10}, \mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_3, \mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_5$