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

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

int p;

int fact(int m)
{
    int pt=5,suma=0;
    while(pt<=m)
    {
        suma+=m/pt;
        pt*=5;
    }
    return suma;
}

int cautbin(int stanga, int dreapta)
{
    if(p==0) return 1;
    int m,s,poz=-1;
    while(stanga<=dreapta)
    {
        m=(stanga+dreapta)/2;
        s=fact(m);
        if(s==p)
            {
               poz=m;
               dreapta=m-1;
            }
        else if(s<p) stanga=m+1;
        else dreapta=m-1;
    }
    return poz;
}

int main()
{
    f>>p;
    g<<cautbin(0,5*p);

    f.close();
    g.close();
    return 0;
}