import sys
input = sys.stdin.readline

N, M = map(int, input().split())
a = [list(map(int, input().split())) for _ in range(N)]

if N==1:
    exit(print(0))
    
dp = a[0][:]

for i in range(1, N):
    ndp = [10**18]*M
    
    for j in range(M):
        ndp[j] = min(ndp[j], dp[j]+a[i][j])
    
    ml = 10**18
    
    for j in range(M):
        ndp[j] = min(ndp[j], ml+a[i-1][j]+a[i][j])
        ml = min(ml, dp[j])
    
    mr = 10**18
    
    for j in range(M-1, -1, -1):
        ndp[j] = min(ndp[j], mr+a[i-1][j]+a[i][j])
        mr = min(mr, dp[j])
    
    dp = ndp

print(min(dp))