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

dp = [INF] * (H - 2)
for i in range(H - 2):
    if A[i][0] != -1:
        dp[i] = A[i][0]
#print(dp)

for i in range(1, W):
    dp2 = [INF] * (H - 2)
    for j in range(H - 2):
        a = A[j][i]
        if a != -1:
            dp2[j] = min(dp2[j], dp[j] + a)
            if 0 < j:
                dp2[j] = min(dp2[j], dp[j - 1] + a)
                dp2[j] = min(dp2[j], dp2[j - 1] + a)
            if j < H - 3:
                dp2[j] = min(dp2[j], dp[j + 1] + a)
    for j in reversed(range(H - 3)):
        a = A[j][i]
        if a != -1:
            dp2[j] = min(dp2[j], dp2[j + 1] + a)
    dp = dp2
    # print(dp)

if min(dp) < INF:
    print(min(dp))
else:
    print(-1)