#include <iostream>
#include <fstream>

using namespace std;

int min(int a,int b)
{
    if (a < b)
        return a;
    return b;
}

int main()
{
    ifstream in("fact.in");

    int p;
    in >> p;

    in.close();

    /*
    while ( (nd,nc) != p && p != 0)
    {
        if (i % 2 == 0)
        {
            nd++;
        }
        if (i % 5 == 0)
        {
            nc++;
        }
        if (i % 25 == 0)
        {
            nc++;
        }
        if (i % 125 == 0)
        {
            nc++;
        }
        if (i % 625 == 0)
        {
            nc++;
        }

        cout << "Nd : " << nd << " nc : " << nc << " for i = " << i << endl;
        i++;
    }
    */

    int minf = p * 5;

    int a = 25;
    int b = 10;

    while (b <= minf)
    {
        minf -=5;
        b *= 10;
    }

    while (a <= minf)
    {
        minf -= 5;
        a *= 5;
    }

    ofstream out;
    out.open("fact.out");

    if (p == 0)
    {
        out << 1 << endl;
    }
    else
    {
        out << minf << endl;
    }


    out.close();

    return 0;
}