#Seive of Eratosthenes
#Finds Prime Numbers

print "Enter the last number to check (greater than 1): "
max_int = gets.to_i
list = (2..max_int).to_a
#(2..Math.sqrt(max_int).to_i).to_a.each do |n|
list.each do |n| #n will only ever be a prime number
puts "Prime Found: #{n}\n Deleting multiples of #{n}..."
        if n**2 > max_int then #Quits once n squared is greater than max_int (only primes will be left)
                puts "Sieve complete..."
                break
        end
       
        list.each_index do |i|
       
                if (list[i] % n == 0) && (list[i] != n) then #Checks if list[i] is divisable by n (but not equal to it, n is prime)
                        #puts "Deleting: #{list[i]}"
                        list.slice!(i) #deletes list[i]
                 end

        end
end

#This won't be necessary later. Once I delete extra puts above I'll delete this.
puts "Primes up to #{max_int}:"
list.each do |i|
        puts i
end