Hi everyone. I do Exercise 4: Get Span From Scores. When I check my result is same as expect value. But when I submit, I have message Code Cell UNQ_C4: Function 'get_span_from_scores is incorrect. Check implementation. I don’t know why i wrong, can anyone explain it ti me . Thanks. This is my code:

```
def get_span_from_scores(start_scores, end_scores, input_mask, verbose=False):
"""
Find start and end indices that maximize sum of start score
and end score, subject to the constraint that start is before end
and both are valid according to input_mask.
Args:
start_scores (list): contains scores for start positions, shape (1, n)
end_scores (list): constains scores for end positions, shape (1, n)
input_mask (list): 1 for valid positions and 0 otherwise
"""
n = len(start_scores)
max_start_i = -1
max_end_j = -1
max_start_score = -np.inf
max_end_score = -np.inf
max_sum = -np.inf
# Find i and j that maximizes start_scores[i] + end_scores[j]
# so that i <= j and input_mask[i] == input_mask[j] == 1
### START CODE HERE (REPLACE INSTANCES OF 'None' with your code) ###
# set the range for i
for i in range(n): # complete this line
# set the range for j
for j in range(1,n): #complete this line
# both input masks should be 1
if input_mask[i] == input_mask[j] == 1: # complete this line
# check if the sum of the start and end scores is greater than the previous max sum
if start_scores[i]+end_scores[j]>max_sum: # complete this line
# calculate the new max sum
max_sum = start_scores[i]+end_scores[j]
# save the index of the max start score
max_start_i = i
# save the index for the max end score
max_end_j = j
# save the value of the max start score
max_start_val = start_scores[i]
# save the value of the max end score
max_end_val = end_scores[j]
### END CODE HERE ###
if verbose:
print(f"max start is at index i={max_start_i} and score {max_start_val}")
print(f"max end is at index i={max_end_j} and score {max_end_val}")
print(f"max start + max end sum of scores is {max_sum}")
return max_start_i, max_end_j
```