#include<fstream.h>
#include<iostream.h>
#include<math.h>
int zerouri(int n,int k)
{
	int s=0;
	if(pow(5,k)<n) s=s+zerouri(n,pow(5,k+1));
	return s;
}
int main()
{
	int p,i=1,ok=0,s;

ifstream fin("fact.in");
ofstream fout("fact.out");
fin>>p;
while(ok==0)
{
	i++; s=0;
	s=zerouri(i,1);
	if(s==p) ok=1;}
fout<<s;
fin.close();
fout.close();
return 0;
}