How many zeros are there at the end of the factorial of 100?

How many zeros are there at the end of the factorial of 100?

After careful calculation, there should be 24 zeros. You will think of trying to multiply. Generally, when you encounter the combination of 2 and 5 at the end, you can get 0. In this way, you can be divided into 10 groups. If you count at least 2 zeros in each group of the whole ten, you can get at least 20 zeros. Now, only some special cases are left to consider. Later, I found that there are only four special cases, respectively