def assert f
  unless f
    puts "Error!: Constraint Violation"
    exit
  end
end

n = gets.to_i
a = gets.split.map(&:to_i)

assert(2 <= n && n <= 500)
a.each do |v|
  assert(1 <= v && v <= 100)
end

f = false
(n-1).times do |i|
  f = true if a[i] == a[i+1]
end
(n-2).times do |i|
  f = true if a[i] == a[i+2]
end
puts f ? "Yes" : "No"