#include <iostream>
#include <fstream>
#define NMAX 1000000000

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");
int p;

int nr0(int key)
{
    int nr = 0;
    for (int i = 5; i <= key; i *= 5)
        nr += (key / i);
    return nr;
}

int binar(int x, int y)
{
    int m;
    while (x <= y)
    {
        m = x + (y - x) / 2;
        if (nr0(m) == p && nr0(m - 1) < p)
            return m;
        else
        {
            if (nr0(m) >= p)
                y = m - 1;
            else
                x = m + 1;
        }
    }
    return -1;
}

int main()
{
    in >> p;
    in.close();
    if (p == 0)
        out << 1 << "\n";
    else
        out << binar(1, NMAX) << "\n";
    out.close();
    return 0;
}