#include <fstream>
using namespace std;

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

int k, n, cnt;

int main()
{
    is >> n;
    if (n == 0)
    {
        os << 1;
        return 0;
    }
    k = 5;
    while (k < n)
    {
        cnt++;
        k *= 5;
    }
    n *= 5;
    cnt *= 5;
    os << n - cnt;
    is.close();
    os.close();
    return 0;
}