#include <iostream>
#include <fstream>

using namespace std;

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

int nrz(int n)
{
    int e = 0;
    while(n >= 5)
    {
        n /= 5;
        e += n;
    }
    return e;
}

int cautbin(int a)
{
    int p = 1, u = 50000000, poz = -1;
    while(p <= u)
    {
        int m = (p + u) / 2;
        int nz = nrz(m);
        if(a == nz)
            poz = m;
        if(a <= nz)
            u = m - 1;
        else p = m + 1;
    }
    return poz;
}

int main()
{
    int P;
    fin >> P;
    fout << cautbin(P);
    fin.close();
    fout.close();
    return 0;
}