#include <fstream>
using namespace std;

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

int Numar_Zero (int numar)
{
    int factor = 5 , zero = 0;
    while (factor <= numar)
        zero += numar / factor , factor *= 5;

    return zero;
}

int main ()
{
    int zero;
    cin >> zero;

    int stanga = 1 , dreapta = 500000000 , numar = 1;
    while (stanga <= dreapta)
    {
        int mijloc = (stanga + dreapta) / 2;

        if (Numar_Zero(mijloc) >= zero)
            dreapta = mijloc - 1 , numar = mijloc;
        else
            stanga = mijloc + 1;
    }

    cout << numar;
    cout.close(); cin.close();
    return 0;
}