import heapq
h, w = map(int, input().split())
a = [list(map(int, input().split())) for _ in range(h-2)]
inf = 1 << 30
dist = [[inf] * w for _ in range(h-2)]
hq = []
for i in range(h-2):
  if a[i][0] == -1:
    continue
  heapq.heappush(hq, [a[i][0], i, 0])
while hq:
  d, x, y = heapq.heappop(hq)
  if y == w - 1:
    print(d)
    exit()
  if dist[x][y] <= d:
    continue
  dist[x][y] = d
  for p in range(max(0, x-1), min(h-2, x+2)):
    for q in range(max(0, y-1), min(w, y+2)):
      if a[p][q] == -1:
        continue
      if dist[p][q] <= d + a[p][q]:
        continue
      heapq.heappush(hq, [d+a[p][q], p, q])
print(-1)