Make a continuous product of natural numbers starting from 1, that is, 1*2*3*4*...*79*80, how many consecutive 0s are there at the end of the product.
把自然数从1开始作连乘积，即1*2*3*4*…*79*80，乘积的末尾有多少个连续的0．
<result>19</result>