# http://projecteuler.net/index.php?section=problems&id=2
# 
# Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
# 
# 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
# 
# Find the sum of all the even-valued terms in the sequence which do not exceed four million.

use strict;
use warnings;

### start values
my $x = 1;
my $y = 2;

### result
my $sum;

while( 1 ) {
    last if $y > 4000000;

    $sum += $y unless $y % 2;   # even number, so add

    my $new = $x + $y;          # compute the new number
    $x = $y;
    $y = $new;
}    

print $sum;