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

   int nrzero(int n)
   {
       long long p=5,c=0;

       while(p<=n){
       c=c+n/p;
       p=p*5;}

    return c;
   }

int main()
{
     long long p;
     int prim=1,ultim=50000000,mijl,sol=-1;
    ifstream f("fact.in");
    ofstream g("fact.out");

f>>p;

   while(prim<=ultim){

    mijl=(prim+ultim)/2;

   if(nrzero(mijl)==p){
    sol=mijl;ultim=mijl-1;}

    if(nrzero(mijl)>p)
     ultim=mijl-1;
    if(nrzero(mijl)<=p)
     prim=mijl+1;
                     }

g<<sol;
}