#!/usr/bin/env luajit
require("utils")
require("pqueue")

local grid = {}
for line in io.lines(arg[3]) do
	local row = {}
	for char in chars(line) do
		table.insert(row, tonumber(char))
	end
	table.insert(grid, row)
end

function printgrid()
	for r, row in pairs(grid) do
		for c, cell in pairs(row) do
			io.write(string.format("%3d", cell))
		end
		io.write('\n')
	end
end

local pq = pqueue(function(a, b)
	return a[3] < b[3]
end)

local distances = {}

local H = math.huge
local n = { 1, 1, 0 }
while n ~= nil and (distances[#grid] == nil or distances[#grid][#grid[1]] == nil) do
	local r, c, d = unpack(n)
	if 0 < r or r <= #grid or 0 < c or c <= #grid[r] then
		local row = distances[r] or {}
		if d < (row[c] or H) then
			row[c] = d
			distances[r] = row
			pq:add({ r-1, c, d + ((grid[r-1] or {})[c] or H) })
			pq:add({ r, c-1, d + ((grid[r] or {})[c-1] or H) })
			pq:add({ r+1, c, d + ((grid[r+1] or {})[c] or H) })
			pq:add({ r, c+1, d + ((grid[r] or {})[c+1] or H) })
		end
	end
	n = pq:pop()
end

print(distances[#grid] and distances[#grid][#grid[1]])