N, M = map(int, input().split())
if N == 1:
    print(0)
    exit()
A = [list(map(int, input().split())) for _ in range(N)]
dp = [0] * M
minc = 10 ** 13
for j in range(M):
    dp[j] = A[0][j] + A[1][j]
    if minc > dp[j]:
        minc = min(minc, dp[j])
        minm = {j}
    elif minc == dp[j]:
        minm.add(j)
for i in range(2, N):
    minc2 = 10 ** 13
    minm2 = {}
    dp2 = [0] * M
    for j in range(M):
        if j in minm:
            tmp = dp[j] + A[i][j]
        else:
            tmp = min(minc + A[i - 1][j] + A[i][j], dp[j] + A[i][j])
        if minc2 > tmp:
            minc2 = tmp
            minm2 = {j}
        elif minc == dp[j]:
            minm2.add(j)
        dp2[j] = tmp
    minc = minc2
    minm = minm2
    dp = dp2
print(minc)