def solve():
    N,M=map(int,input().split())
    A=[]
    for _ in range(N):
        A.append(list(map(int,input().split())))

    if N==1:
        return 0

    inf=float("inf")
    T=0
    DP=[inf]*M
    for i in range(N-1):
        E=DP
        DP=[inf]*M
        Ai=A[i]; Aii=A[i+1]
        for j in range(M):
            DP[j]=min(E[j]+Aii[j], T+Ai[j]+Aii[j])
        T=min(DP)

    return T

#==================================================
print(solve())