h, w = map(int, input().split())
h -= 2
a = [list(map(int, input().split())) for _ in range(h)]
INF = 10**18
dp = [[INF] * w for _ in range(h)] + [[INF] * w]

for i in range(h):
    if a[i][0] == -1:
        continue
    dp[i][0] = a[i][0]

for j in range(w - 1):
    for i in range(h):
        if a[i][j + 1] == -1:
            continue
        dp[i][j + 1] = min(dp[i - 1][j], dp[i][j], dp[i + 1][j]) + a[i][j + 1]
ans = min(v[-1] for v in dp)
print(ans if ans < INF else -1)
# print(*dp, sep="\n")