R,C = [int(x) for x in input().split()]

suma = 0
arr = []

for i in range(R):
    arr.append(list(map(int, input().split())))
    suma += sum(arr[-1])

if R%2 == 0 and C%2 == 0:
    
    suma -= min(arr[-1][-2], arr[-2][-1])

print(suma)