#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 = 100000000, poz = -1;
    while(p <= u)
    {
        int m = (p + u) / 2;
        if(a <= nrz(m))
        {
            poz = m;
            u = m - 1;
        }
        else
            p = m + 1;
    }
    return poz;
}
int main()
{
    int P;
    f>>P;
    g<<cautbin(P);
    return 0;
}