#include<fstream>
using namespace std;

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

int f(int n)//numarul de zerouri ale lui n!
{
    int k = 5, nr = 0;

    while(n / k)
    {
        nr += n/k;
        k *= 5;
    }

    return nr;
}

int main()
{
    int n, p, li, ls, ok, t;

    fin >> p;

    li = 1; ls = 1000000000; ok = 0;

    while(li <= ls && !ok)
    {
        n = (li + ls)/2;
        t = f(n);

        if(t == p) ok = 1;
        else if(t < p) li = n + 1;
             else ls = n - 1;
    }

    if(ok)
    {
        while(n > 0 && f(n-1) == p) n--;

        fout << n;
    }
    else fout << -1;

    fin.close(); fout.close();

    return 0;
}