#include <fstream>
#include <iostream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
   int main()
  {
     long long n,k=1,i,f=0,h=5,x=1;
     in>>n;
     if(n==0)
     {
       out<<"1";
       return 0;

     }
     for(i=1;k<=n;i++)
     {
         k=5*k;
         if(k==n)
         {
             out<<"-1";
             return 0;
         }
         if(k>n)
         {
            out<<n*5-f;
            return 0;
         }


           f=f+x*h;
           x++;

     }

     out<<"-1";
     return 0;

  }