#! perl -wl
my $string = '423RY75Y69827EC67592C78657N965R345U299M';
my $correct = '423R_Y75Y_69827E_C67592C_78657N965R_345U_299M';
$string =~ s/([A-MO-Z])([A-MO-Z]*[\dN]+)/$1_$2/g;
print $string eq $correct' ? 'OK' : 'NOT OK';