res = "T"
previous = nil
(1..gets.chomp.to_i).each do |i|
    v = gets.chomp.to_i
    if i == 1 and v.abs != 1
       res = "F"
       break
    elsif previous.nil? == false and (previous - v).abs != 1
        res = "F"
        break
    end
    previous = v
end
puts res