local gx, gy = io.read("*n", "*n")
gx, gy = gx + 1, gy + 1
local n, f = io.read("*n", "*n")

local len = {}
for h = 1, gy do
  for w = 1, gx do
    len[(h - 1) * gx + w] = (h + w - 2) * f
  end
end
for i = 1, n do
  local x, y, c = io.read("*n", "*n", "*n")
  for h = gy - y, 1, -1 do
    for w = gx - x, 1, -1 do
      local src = (h - 1) * gx + w
      local dst = (h - 1 + y) * gx + w + x
      if len[src] + c < len[dst] then
        len[dst] = len[src] + c
      end
    end
  end
end
local ret = (gx + gy - 2) * f
for h = 1, gy do
  for w = 1, gx do
    ret = math.min(ret, len[(h - 1) * gx + w] + (gy - h + gx - w) * f)
  end
end
print(ret)