#include <fstream>

using namespace std;

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

int p;
int be, en, mid;

int exponent5(int n)
{
    int nr=0;
    int x=1;
    while (x<=n)
      x*=5;
    x/=5;
    while (x>=5)
    {
        nr+=n / x;
        x/=5;
    }
    return nr;
}

int cautbin()
{
    int be=1;
    int en=p*5;
    int ans=-1;
    while (be<=en)
    {
        mid=(be+en) / 2;
        if (exponent5(mid)>=p)
        {
            if (exponent5(mid)==p)
              ans=mid;
            en=mid-1;
        }
        else
          be=mid+1;
    }
    return ans;
}

int main()
{
    fin >> p;
    if (p>0)
      fout << cautbin();
    else
      fout << 1;
    fin.close();
    fout.close();
    return 0;
}