awk '
    BEGIN{xmin=999;xmax=-999;ymin=999;ymax=-999}
    $1=="m"||$1=="n"{
	if($2>xmax)xmax=$2;
	if($2<xmin)xmin=$2;
	if($3<ymin)ymin=$3;
	if($3>ymax)ymax=$3
    }
    END{print xmin, xmax, ymin, ymax}' $*
