n, m = map(int, input().split()) board = [list(map(int, input().split())) for _ in range(n)] prefix_sum = [[0] * (m + 1) for _ in range(n + 1)] for i in range(1, n + 1): for j in range(1, m + 1): prefix_sum[i][j] = prefix_sum[i - 1][j] + prefix_sum[i][j - 1] + \ board[i - 1][j - 1] - prefix_sum[i - 1][j - 1] def acc(mat, x1, y1, x2, y2): return mat[x2][y2] - mat[x1 - 1][y2] - mat[x2][y1 - 1] + m..