use strict;
use warnings;

my $startPop = 4;
my $targetPop = 250e9;
my $increase = 2.5;
my $n = int ((log($targetPop) - log($startPop)) / log($increase) + 0.5);
my $pop = int ($startPop * ($increase) ** $n);

print "$pop population after $n generations\n";

##</code><code>##

222044604925 population after 27 generations