#include <fstream>
using namespace std;
ifstream in ("fact.in");
ofstream out ("fact.out");
int f(int a)
{
    int x=5,s=0;
    while(x<=a)
    {
        s=s+a/x;
        x=x*5;
    }
    return s;
}
int main()
{
    int st=0,x,dr=2000000000,p,n=-1;
    long long mij;
    in>>p;
    if(p==0)
        out<<"1";
    while(st<=dr)
    {
         mij=(st+dr)/2;
         if(f(mij)>p)
         {
             dr=mij-1;
         }
         if(f(mij)<p)
         {
             st=mij+1;
         }
         if(f(mij)==p)
            n=mij,dr=mij-1;}
          out<<n;
    return 0;
}