8279번 - Double Factorial 다국어

For a positive integer n, its factorial is defined as the product of all integers from 1 to n, denoted as n!. Now n double factorial is the product of 1 factorial, 2 factorial, ..., up to n factorial: 1! · 2! · 3! · ... · n!. Given n, find the number of trailing zeros of a decimal representation of n double factorial.

The first and only line of the standard input contains an integer n (1 ≤ n ≤ 10¹⁸).

The first and only line of the standard output should contain the number of trailing zeros of n double factorial.

11 double factorial equals 265 790 267 296 391 946 810 949 632 000 000 000. This number has 9 trailing zeros.