#include<iostream.h>
#include<fstream.h>
long i,p,pr,s;
 ifstream fin("fact.in");
 ofstream fout("fact.out");
int main()
{
	fin>>p;
	i=0;
	do
	{
		s=0;
		pr=1;
		i=i++;
		do
		{
			pr=pr*5;
			s=s+i/pr;
		}
		while(pr<=i);
	}
	while(s<p);
	fout<<i<<endl;
return 0;
}