#include <iostream>
#include <fstream>
using namespace std;

ifstream f;
ofstream g;

long int q,z,n,k,p,i;

long int fact(long int p)
        {
        int k=0;
        n=0;
        int i;
         while(k<p){
           n+=5;
           i=n;
           while(i%5==0){k++;i/=5;}
           }

           return k;
        }

void ficti(long int a,long int b)
        {

         q=(a+b)/2;
	 z=fact(q);
         if(a+1==b)g<<-1;
	 	else
                {
         if(z>p)ficti(a,q);
         else if(z<p)ficti(q+1,b);
         else g<<n;
                }
        }


main()
{

f.open("fact.in");
g.open("fact.out");

f>>p;
n=0;
k=0;

ficti(0,10000);
g.close();
}