import itertools as iter
import collections as coll
import heapq as hq
import bisect as bis
from decimal import Decimal as dec
from functools import cmp_to_key
import math
import sys
#import pypyjit
#pypyjit.set_param('max_unroll_recursion=-1')
sys.setrecursionlimit(10 ** 6)
inp = sys.stdin.readline
input = lambda : inp().rstrip()
getN = lambda : int(inp())
getNs = lambda : map(int, inp().split())
getList = lambda :list(map(int, inp().split()))
getStrs = lambda n : [input() for _ in [0] * n]
def yexit(): print("Yes"); exit(0)
def nexit(): print("No"); exit(0)
pi = 3.141592653589793
mod = 1000000007
MOD = 998244353
INF = 4611686018427387903
dx = [1, 0, -1, 0];	dy = [0, 1, 0, -1]
#di = coll.defaultdict(int)


"""
Main Code
"""

n, m = getNs()
a = [getList() for _ in [0]*n]

dp = [[[INF]*2 for _ in [0]*m] for _ in [0]*n]
dp[0][0][0] = 0
que = [(0,0,0,0)]
while(que):
	#print(que)
	c,p,q,r = hq.heappop(que)
	if(c > dp[p][q][r]):
		continue
	if(p == n - 1):
		print(c)
		break
	if(q > 0 and c < dp[p][q-1][0]):
		dp[p][q-1][0] = c
		hq.heappush(que, (c,p,q-1,0))
	if(q < m - 1 and c < dp[p][q+1][0]):
		dp[p][q+1][0] = c
		hq.heappush(que, (c,p,q+1,0))
	if(r == 0):
		nc = c + a[p][q]
		if(nc >= dp[p][q][1]):
			continue
		dp[p][q][1] = nc
		hq.heappush(que, (nc,p,q,1))
	else:
		nc = c + a[p+1][q]
		if(nc >= dp[p+1][q][1]):
			continue
		dp[p+1][q][1] = nc
		hq.heappush(que, (nc,p+1,q,1))