#include <iostream>
#include <fstream>

using namespace std;

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

int P; //numarul intreg

int factorial_zero(int P)
{
    int zerouri = 0;
    int numar = 1;
    bool iesire = false;
    bool corect = false;

    while (!iesire && !corect)
    {
        int copie_numar = numar;
        while (copie_numar / 5 != 0 && zerouri <= P)
        {
            zerouri += copie_numar / 5;
            copie_numar /= 5;
        }

        if(zerouri > P)
        {
            iesire = true;
        }
        else if(zerouri == P)
        {
            corect = true;
        }
        else {
            numar++;
            zerouri = 0;
        }
        
    }

    if(iesire == true)
        return -1;
    else
        return numar;  
}


int main()
{
    in >> P;
    out << factorial_zero(P);
    return 0;
}