Simple Calculator in Ruby

puts "Enter the first number"
first=gets.chomp().to_f
puts "Enter the second number"
second=gets.chomp().to_f
op=""
while (op!=5)
 puts "Enter the operation you wish to perform"
 puts "1.Addition\n2.Subtraction\n3.Multiplication\n4.Division\n5.Exit"
 op=gets.chomp()
 if op=="1"
   sum=first+second
   puts "The addition of two numbers is "+sum.to_s
 elsif op=="2"
   sub=first-second
   puts "The subtraction of two numbers is "+sub.to_s
 elsif op=="3"
   mul=first*second
   puts "The multiplication of two numbers is "+mul.to_s
 elsif op=="4"
   div=first/second
   puts "The division of two numbers is "+div.to_s
 elsif op=="5"
   exit
 else
   puts "Invalid Selection"
 end
end