def solve(a)
  return (0...N).any? {|i|
    a.each_with_index.all? {|j, k| k < i ? j <= k + 1 : j <= N - k + i}
  }
end
N = gets.to_i
a = gets.split.map &:to_i
puts solve(a) || solve(a.reverse) ? "Yes" : "No"