#include <iostream>
#include <fstream>
using namespace std;
int p,n;
int a[13]={25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625,1220703125};
int b[13]={1,   2,  3,   4,    5,    6,     7,      8,      9,      10,       11,        12};
int main ()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	fin>>p;
	if (p==0) fout<<"1";
	else
	{
		int i=11;
		n=p*5;
		while (n<a[i])
			i--;
		n-=b[i]*5;
		fout<<n;
	}
	return 0;
}