local mmi, mma = math.min, math.max
local h, w = io.read("*n", "*n", "*l")
local a = {}
for i = 1, h do
  a[i] = {}
  local s = io.read()
  for b in s:gmatch("(%d+)") do
    table.insert(a[i], tonumber(b))
  end
end
if h == 1 then
  print(0)
  os.exit()
end
local dp1, dp2 = {}, {}
for i = 1, w do
  dp1[i] = a[1][i]
end
for i = 1, h - 1 do
  local src = i % 2 == 1 and dp1 or dp2
  local dst = i % 2 == 1 and dp2 or dp1
  local minpos = 1
  for j = 2, w do
    if src[j] <= src[minpos] then
      minpos = j
    end
  end
  local minval = src[minpos]
  for j = 1, w do
    if j ~= minpos then
      src[j] = mmi(src[j], minval + a[i][j])
    end
  end
  for j = 1, w do
    dst[j] = src[j] + a[i + 1][j]
  end
end
local tbl = h % 2 == 0 and dp2 or dp1
local ans = tbl[1]
for i = 2, w do
  ans = mmi(ans, tbl[i])
end
print(ans)