import sys
readline = sys.stdin.readline

class SegmentTree:
    def __init__(self, size, f=min, default=10 ** 18):
        self.size = 2**(size-1).bit_length() 
        self.default = default
        self.dat = [default]*(self.size*2) 
        self.f = f

    def update(self, i, x):
        i += self.size
        self.dat[i] = x
        while i > 0:
            i >>= 1
            self.dat[i] = self.f(self.dat[i*2], self.dat[i*2+1])

    def query(self, l, r):
        l += self.size
        r += self.size
        lres, rres = self.default, self.default
        while l < r:
            if l & 1:
                lres = self.f(lres, self.dat[l])
                l += 1

            if r & 1:
                r -= 1
                rres = self.f(self.dat[r], rres) 
            l >>= 1
            r >>= 1
        res = self.f(lres, rres)
        return res
    

N, M = map(int, readline().split())
if N == 1:
    print(0)
    exit()
A = []
for i in range(N):
    A.append(list(map(int, readline().split())))
A.append([0]*M)

pre = SegmentTree(M)
for i in range(M):
    pre.update(i, A[0][i] + A[1][i])
    
for i in range(1, N):
    dp = SegmentTree(M)
    for j in range(M):
        now = pre.query(j, j + 1)
        pre.update(j, now - A[i][j])
        dp.update(j, pre.query(0, M) + A[i][j] + A[i + 1][j])
        pre.update(j, now)
    pre, dp = dp, pre
    
print(pre.query(0, M))