#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long m;
int n,p;
int nr_cif_0(int m)
{
    if(m==0)
        return 1;
    int d,i,nr2=0,nr5=0;
    for(i=1;i<=m;i++)
    {
        if(i%2==0){
            d=i;
            while(d%2==0){
                nr2++;
                d=d/2;}
            }
        if(i%5==0){
            d=i;
            while(d%5==0){
                nr5++;
                d=d/5;
            }
        }
    }

    return min(nr2,nr5);
}
int main()
{
    f>>p;
    int st=0, dr=1e8, ok=0;
    while(st<dr&&ok==0)
    {

        m=(st+dr)/2;
        if(nr_cif_0(m)>p&&ok==0)
            dr=m-1;
        else
            if(nr_cif_0(m)<p)
              st=m+1;
            else
                ok=1;

    }
    if(ok==1)
    {
      while(nr_cif_0(m-1)==p)
        m--;
        g<<m;
    }
    else g<<"-1";

    return 0;
}