#!/bin/ruby

n = gets.strip.to_i
a = gets.strip
a = a.split(' ').map(&:to_i)
result = 0
flag = 1
a.each_with_index do |x, i|
    a.drop(flag).each_with_index do |y, c|
        if (x - y).abs <= 1
            result += 1
            break
        end
    end
    flag += 1
end
print result