N, P = gets.split.map(&:to_i)
H = gets.split.map(&:to_i)

dp = Array.new(N) { Array.new(2, Float::INFINITY) }

dp[0][0] = 0
dp[0][1] = 0

1.upto(N - 1) do |i|
  bh = H[i - 1]
  h = H[i]

  cost1 = dp[i - 1].min + P
  cost2 = dp[i - 1][0] + [0, h - bh].max
  cost3 = dp[i - 1][1] + [0, bh - h].max

  dp[i][0] = [cost1, cost2].min

  if i > 1
    dp[i][1] = [cost1, cost3].min
  else
    dp[i][1] = cost1
  end
end

puts dp[N - 1].min