#include <iostream>
#include <fstream>
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

int nrz(int x)
{
    int e = 0, p = 5;
    while(x >= p)
    {
        e += x / p;
        p *= 5;
    }
    return e;
}
int cautbin(int a)
{
    int p = 1, u = 400000000, poz = -1;
    while(p <= u)
    {
        int m = (p + u) / 2;
        int nt = nrz(m);
        if(a == nt)
            poz = m;
        if(a <= nt)
            u = m - 1;
        else
            p = m + 1;
    }
    return poz;
}
int main()
{
    int P;
    f >> P;
    g << cautbin(P);
    return 0;
}