#include<fstream>
using namespace std;
long n,d,s,m,x,p;
int main()
{
	ifstream f("fact.in");ofstream g("fact.out");
	f>>n;
	if(n==0)g<<1;
	  s=1;d=420000000;
	while(s<=d)
	 {
		 m=(s+d)/2;
		if(m/5+m/25==n){s=d+1;x=m;}
		 else
	    if(m/5+m/25>n)d=m-1;
		 else s=m+1;
	 }
	g<<(x/5)*5;
	f.close();g.close();
return 0;}