from collections import deque
h, w = map(int, input().split())
a = [[] for _ in range(h - 2)]
for i in range(h - 2):
    a[i] = list(map(int, input().split()))
ans = 800 * 801
for i in range(h - 2):
    if a[i][0] == -1: continue
    q = deque()
    q.append((i, 0, a[i][0]))
    while q:
        tate, yoko, cost = q.popleft()
        if yoko == w - 1:
            if ans > cost:
                ans = cost
            continue
        for j in range(-1, 2):
            if h - 3 >= tate + j >= 0 and a[tate + j][yoko + 1] != -1:
                q.append((tate + j, yoko + 1, cost + a[tate + j][yoko + 1]))
if ans == 800 * 801:
    print(-1)
else:
    print(ans)