from heapq import *

H, W = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(H - 2)]
INF = 10 ** 9

D = [[INF] * (H - 2) for _ in range(W)]
q = []
dir = [[0, 1], [1, 1], [1, 0], [1, -1], [0, -1], [-1, -1], [-1, 0], [-1, 1]]

for i in range(H - 2):
    a = A[i][0]
    if a != -1:
        heappush(q, (a, (0, i)))
        D[0][i] = a

while q:
    d, (x, y) = heappop(q)
    if d > D[x][y]:
        continue
    for xd, yd in dir:
        xd += x
        yd += y
        if 0 <= xd < W and 0 <= yd < H - 2 and A[yd][xd] != -1:
            if D[xd][yd] > D[x][y] + A[yd][xd]:
                D[xd][yd] = D[x][y] + A[yd][xd]
                heappush(q, (D[xd][yd], (xd, yd)))

ans = min(D[-1])
if ans == INF:
    print(-1)
else:
    print(ans)