The input is a natural number n — the number of rows and columns in the matrix, the number of matrix elements (integers) line by line separated by a space. draw the maximum element below the main diagonal. The elements of the main diagonal are also taken into account.

def max_matrix_element(n):
    if n < 2:
        return None
    matrix = []
    for i in range(n):
        matrix.append(list(map(int, input().split())))
    for i in range(n-1):
        for j in range(n-1):
            if matrix[i][j] < matrix[j][i] and i > j:
                matrix[i][j] = -1
    return matrix    
    
max_matrix_element(3)