from heapq import heappop, heappush


h, w = map(int, input().split())
a = [list(map(int, input().split())) for _ in range(h - 2)]

# 最小カットするのは面倒なので、左から右にpathを通して切る
distance = [[-1] * w for _ in range(h - 2)]
heap_queue = []

for i in range(h - 2):
    if a[i][0] >= 0:
        heappush(heap_queue, (a[i][0], i * w))

while len(heap_queue):
    d, ij0 = heappop(heap_queue)
    i0, j0 = ij0 // w, ij0 % w
    if distance[i0][j0] == -1:
        distance[i0][j0] = d
    else:
        continue
    
    # 8方向にpath
    for i1 in range(max(0, i0 - 1), min(h - 2, i0 + 2)):
        for j1 in range(max(0, j0 - 1), min(w, j0 + 2)):
            if i1 == i0 and j1 == j0:
                continue
            if a[i1][j1] >= 0 and distance[i1][j1] == -1:
                heappush(heap_queue, (distance[i0][j0] + a[i1][j1], i1* w + j1))

res_list = [distance[i][-1] for i in range(h - 2)]
if max(res_list) == -1:
    print(-1)
else:
    print(min([r for r in res_list if r >= 0]))