Roboticus@Roboticus-PC ~
$ cat foo.pl
#!/usr/bin/perl
use strict;
use warnings;

for my $str ('AD 1650', '16.50', '1650') {
   my $num = $str + 0;  # Convert to a number
   my $int = int($num); # Convert to an int
   print "string=$str, number=$num, integer=$int.\n";
}

Roboticus@Roboticus-PC ~
$ perl foo.pl
Argument "AD 1650" isn't numeric in addition (+) at foo.pl line 6.
string=AD 1650, number=0, integer=0.
string=16.50, number=16.5, integer=16.
string=1650, number=1650, integer=1650.