#include <iostream>
#include <fstream>


using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int main()
{
    long p,aux=-1,st=0,dr=100000000,s=0,i,m;
    fin>>p;
    if (p==0)
           aux=1;
    else
           while(st<=dr)
                        {
                            m=(st+dr)/2;
                            s=0;
                            i=5;
                            while(m/i>=1)
                               {
                                   s+=m/i;
                                   i*=5;
                               }
                            if(s==p)
                               {
                                aux=m;
                                dr=m-1;
                               }
                            else
                                if(s>p) dr=m-1;
                                else st=m+1;


                        }
   fout<<aux;
   return 0;
}