#include <fstream>

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

int nr5(int,int );

int main()
{
    long n,i=0,k=0,p=0;
    fin>>n;

    while ( k<=n )
    {
        p=0;
        i++;
        p=nr5(i,k);
        if ( p )
            k=p;

    }
    fout<<i-5;
    fin.close();
    fout.close();
    return 0;

}

int nr5 ( int a , int k)
{
    int i=0;
    //fout<<"in functie intra "<<a<<" si "<<k<<" iar functia returneaza ";
    while (a%5==0)
    {
            i++;
            a=a/5;
    }
    if (i)
    {
        //fout<<i+k<<"\n";
        return i+k;
    }
    else
    {
        //fout<<"0\n";
        return 0;
    }
}