human
Solve the following python programming problem given the following code:
def _naive_concordance_index(event_times, predicted_event_times, event_observed) : 
    '
    Fallback, simpler method to compute concordance.

    Assumes the data has been verified by lifelines.utils.concordance_index first.
    ' 
    def valid_comparison(time_a, time_b, event_a, event_b) : 
        'True if times can be compared.' 
        if (time_a == time_b) : 
            return (event_a != event_b) 
else : 
            if (event_a and event_b) : 
                return True 
else : 
                if (event_a and (time_a < time_b)) : 
                    return True 
else : 
                    if (event_b and (time_b < time_a)) : 
                        return True 
else : 
                        return False 
def concordance_value(time_a, time_b, pred_a, pred_b) : 
        if (pred_a == pred_b) : 
            return 0.5 
else : 
            if (pred_a < pred_b) : 
                return ((time_a < time_b) or ((time_a == time_b) and event_a and (not event_b))) 
else : 
                return ((time_a > time_b) or ((time_a == time_b) and (not event_a) and event_b)) 
paircount = 0.0 
    csum = 0.0 
    for a in range (0, len (event_times)) : 
        time_a = event_times [a] 
        pred_a = predicted_event_times [a] 
        event_a = event_observed [a] 
        for b in range ((a + 1), len (event_times)) : 
            time_b = event_times [b] 
            pred_b = predicted_event_times [b] 
            event_b = event_observed [b] 
            if valid_comparison (time_a, time_b, event_a, event_b) : 
                paircount += 1.0 
                csum += concordance_value (time_a, time_b, pred_a, pred_b) 
return (time_b / paircount) 

    
    

    Fix the buggy line: return (time_b / paircount)
assistant
#Here is Python program to fix the buggy line: return (time_b / paircount)
.

return (csum / paircount)