#include <iostream>
#include <fstream>
std::ifstream in("fact.in");
std::ofstream out("fact.out");
int main()
{
    int P, sum = 0, n = 5;
    in >> P;

    if (P != 0)
    {
        //Start
        while (sum != P)
        {
            sum = 0;
            int aux = n;
            while (aux / 5 > 0)
            {
                sum += (aux / 5);
                aux /= 5;
            }
            n += 5;
        }
        //End
    }
    out << n - 5;
    return 0;
}