def main():
    import sys
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx])
    idx += 1
    M = int(input[idx])
    idx += 1
    if N == 1:
        print(0)
        return
    A = []
    for _ in range(N):
        row = list(map(int, input[idx:idx+M]))
        idx += M
        A.append(row)
    
    # Initialize DP
    dp_prev = [0] * M
    for j in range(M):
        dp_prev[j] = A[0][j] + A[1][j]
    
    for i in range(N-2):
        current = [float('inf')] * M
        min_prev = min(dp_prev)
        for j in range(M):
            # Option 1: extend the interval in j
            if i + 2 < N:
                option1 = dp_prev[j] + A[i+2][j]
            else:
                option1 = float('inf')
            # Option 2: start new interval in j
            option2 = min_prev + A[i+1][j] + (A[i+2][j] if i+2 < N else 0)
            current[j] = min(option1, option2)
        dp_prev = current
    
    print(min(dp_prev))

if __name__ == '__main__':
    main()