#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int nrz(int n)
{
    int ex = 0, pp = 5;
    while(n >= pp)
    {
        ex += n / pp;
        pp *= 5;
    }
    return ex;
}
int cautbin(int a)
{
    int p = 1, u = 1000000000, poz = -1;
    while(p <= u)
    {
        int m = p + (u - p) / 2;
        int nz = nrz(m);
        if(nz == a)
        {
            poz = m;
            u = m - 1;
        }
        else
            if(nz > a)
                u = m - 1;
            else
                p = m + 1;
    }
    return poz;
}
int main()
{
    int p;
    f >> p;
    g << cautbin(p);
    return 0;
}