h, w = map(int, input().split())
A = []
A.append([-1 for _ in range(w)])
for _ in range(h - 2):
    A.append(list(map(int, input().split())))
A.append([-1 for _ in range(w)])

INF = 10**18
DP = [[INF for _ in range(w)] for _ in range(h)]
for i in range(h):
    if A[i][0] != -1:
        DP[i][0] = A[i][0]
for j in range(w - 1):
    for i in range(h):
        if DP[i][j] == INF:
            continue
        for di in (-1, 0, 1):
            ni = i + di
            if A[ni][j + 1] == -1:
                continue
            DP[ni][j + 1] = min(DP[ni][j + 1], DP[i][j] + A[ni][j + 1])
ans = INF
for i in range(h):
    ans = min(ans, DP[i][w - 1])
if ans == INF:
    ans = -1
print(ans)