#include<fstream>

using namespace std;

unsigned long p,n,k,i,f;
int main()
{  ifstream fin("fact.in");
   ofstream fout("fact.out");
   fin>>p;
   n=p*5;
   while(f!=p)
   { k=0;
     i=5;
     while(n/i>=1)
     {  k=k+n/i;
        i=i*5;
     }
     n-=5;
     f=k; 
   }  
   if(f==p)   fout<<n+5; 
              else fout<<-1; 
   fin.close();
   fout.close();
}