The input is a natural number n — the number of rows and columns in the square matrix. Next, the elements of the matrix are entered line by line with a space. Output the maximum element excluding the area above the main diagonal.

def find_max_exluding_main_diagonal(matrix):
    rows, columns = len(matrix), len(matrix[0])
    max_num = matrix[0][0]
    for i in range(1, rows):
        for j in range(i):
            if max_num < matrix[i][j]:
                max_num = matrix[i][j]
    return max_num

# Test
matrix = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]
find_max_exluding_main_diagonal(matrix)