#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int main()
{
    int n, k=0, p, pm;
    fin >> p;
    n = 4*p;
    pm = 5;
    while(n/pm)
    {
        k += n/pm;
        pm *= 5;
    }
    n = 5*(n/5 + 1);
    do
    {
        pm = 5, k = 0;
        while(n/pm)
        {
            k += n/pm;
            pm *= 5;
        }
        n+=5;
    } while(k<p);
    n -= 5;
    if(p==0)
        fout << 1;
    else if(k==p)
        fout << n;
    else
        fout << k;
    fin.close();
    fout.close();
    return 0;
}