n = gets.to_i
a = gets.split.map(&:to_i)
a.sort!
a.push(0)
count = 0
i = 0
while i < n
    c = a[i]
    s = i
    i += 1
    while c == a[i] do
        i += 1
    end
    if s + 1 == i
        count += 1
    end
end
puts count