leap-year or not ?

# Fact: A year is a leap year if it is divisible by 4, unless it is divisible by 100. However, years divisible by 400 are leap years.

puts "Please enter the four digit Year "
year_string = gets.chomp
puts "You have entered , YEAR : " + year_string
# convert the inputted string into integer
year_integer=year_string.to_i

if year_integer<1000
puts "Invalid input!! Please reenter a 4 digit number"
exit
end

if( ( ( year_integer%4==0) and ( year_integer%100 != 0 ) ) or (year_integer%400 == 0 ) )
puts "Its a leap year."
else
puts "Its not a leap year"
end