by@kurgm
AC
594ms
<?php for($x=[],$i=5;--$i;)$x=array_merge($x,fgetcsv(STDIN,9," "));for(;$i<9;)$a+=($i>5)*($x[$i]-=$x[$i+3])*($x[3-~$i%3]*$x[$t=~-$i%3]-$x[++$i%3]*$x[$t+3]);echo$a/6;
60 28 67 01 13 01 29 31 58 10 56 21
9217
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