#include<fstream>
using namespace std;
long long p,m;
int verifica(long long k)
{    
    int nr=0;       
    while(k)
        {          
            nr=nr+k/5;
            k=k/5;
        }
        return nr;
}
void caut(long long st,long long dr,long long x)
     
{
    long gasit=0;
    while(st<=dr&&!gasit)
    {
        m=(st+dr)/2;
        if(verifica(m)==x)
           gasit=1;             
          else
            if(x>verifica(m))        
           st=m+1;
           else                          
            dr=m-1; 
       
    }
    if(gasit==0)
    m=-1;   
}
   int main()
{
	ifstream f("fact.in");   
    ofstream g("fact.out");
    f>>p;
    caut(1,999999999,p);
    if(m!=-1)
    {
        while(m)
       {
            if(verifica(m)==p)
            m--;
            else
            break;
        }
        g<<m+1;
   }            
   else
    g<<m;
return 0;
     
}