# First Bloop program
# If you put this in a file called "bloop1.rb" then you can run it
# with an argument from the keyboard, e.g., typing
# ruby bloop1.rb 2 will compute hyperexp(2)


# successor is the only initial function
def s(n)
   return(n + 1)
end

# plus is defined by repeatedly applying s
def plus(a,b)
    a.times do
       b = s(b)
    end
    return(b)
end

# mult is defined by repeatedly applying plus
def mult(a,b)
    ans = 0
    a.times do
       ans = plus(b,ans)
    end
    return(ans)
end

# exp is defined by repeatedly applying times
def exp(a,b)
    ans = 1
    b.times do
       ans = mult(a,ans)
    end
    return(ans)
end

# hyperexp is defined by repeatedly applying exp(2,x)
def hyperexp(a)
    ans = 1
    a.times do
       ans = exp(2,ans)
    end
    return(ans)
end


a = ARGV[0].to_i
print "hyperexp( #{a} ) = #{hyperexp(a)} \n "