Python嵌套列表中的索引

我有一个嵌套列表

fl = [[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]], 
    [[21, 22, 23, 24, 25, 26, 27, 28, 29, 30], [31, 32, 33, 34, 35, 36, 37, 38, 39, 40]], 
    [[41, 42, 43, 44, 45], [46, [47, 48], 49, 50], [51, 52, 53, 54, 55], [56, 57, 58, 59, 60]],
    [[61, 62, 63, [64, 65, 66, 67, 68, 69, 70, 71], 72, 73, 74, [75, [76, 77, 78], 79], 80]], 
    [[81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100]]]

What i need to do is to input a value from a fl (the list) and get list of indexes:

indices = [] #will try
example = int(input('Choose from a list - ')) 
for i in range (len(fl)):
    for j in range (len(fl[i])):
        for k in range(len(fl[i][j])):
            if fl[i][j][k] == example:
                    indices.append(i)
                    indices.append(j)
                    indices.append(k)
print(indices)

但是对于某些包含的列表(例如[47,48]),它没有任何答案。如果

for l in range(len(fl[i][j][k])):

被添加到无法正常工作的代码中。如何获得指数?