n, m = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(n)]
if n == 1:
    print(0)
    exit()

INF = 10**18
DP = [[INF for _ in range(m)] for _ in range(n - 1)]
prev_min_c = INF
prev_min_c_pos = set()
for i in range(m):
    DP[0][i] = A[0][i] + A[1][i]
    if DP[0][i] < prev_min_c:
        prev_min_c = DP[0][i]
        prev_min_c_pos = set([i])
    elif DP[0][i] == prev_min_c:
        prev_min_c_pos.add(i)
for i in range(2, n):
    curr_min_c = INF
    curr_min_c_pos = set()
    for j in range(m):
        if j in prev_min_c_pos:
            DP[i - 1][j] = min(DP[i - 2][j] + A[i][j], prev_min_c + A[i][j])
        else:
            DP[i - 1][j] = min(DP[i - 2][j] + A[i][j], prev_min_c + A[i][j] + A[i - 1][j])
        if DP[i - 1][j] < curr_min_c:
            curr_min_c = DP[i - 1][j]
            curr_min_c_pos = set([j])
        elif DP[i - 1][j] == curr_min_c:
            curr_min_c_pos.add(j)
    prev_min_c = curr_min_c
    prev_min_c_pos = curr_min_c_pos
print(min(DP[-1]))