#include <iostream>
#include <fstream>

using namespace std;

int factorial(int n)
{
    if (n == 0)
        return 1;
    return n * factorial(n - 1);
}

int countDigits(int n)
{
    int s = 0;
    while (n)
    {
        if (n % 10 == 0)
            s += 1;
        else break;
        n /= 10;
    }
    return s;
}

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

    int n;
    f>>n;

    long long i = 0, result;
    while (true)
    {
        result = countDigits(factorial(i));
        if (result == (long long) n)
        {
            g<<i;
            break;
        }
        i++;
    }


    return 0;
}