h, w = map(int, input().split())
a = [list(map(int, input().split())) for _ in range(h-2)]
inf = 1 << 30
dp = [[inf] * (h - 2) for _ in range(w)]
for i in range(h-2):
  if a[i][0] == -1:
    continue
  dp[0][i] = a[i][0]
for j in range(1, w):
  for i in range(h-2):
    if a[i][j] == -1:
      continue
    for k in range(max(0, i-1), min(h-2, i+2)):
      dp[j][i] = min(dp[j][i], dp[j-1][k]+a[i][j])
    x = a[i][j]
    for k in reversed(range(i-1)):
      if a[k+1][j] == -1:
        break
      x += a[k+1][j]
      dp[j][i] = min(dp[j][i], dp[j-1][k]+x)
    x = a[i][j]
    for k in range(i+2, h-2):
      if a[k-1][j] == -1:
        break
      x += a[k-1][j]
      dp[j][i] = min(dp[j][i], dp[j-1][k]+x)
print(min(dp[-1]) if min(dp[-1]) < inf else -1)