#include <fstream>
using namespace std;
int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    long n=0, p;
    long i, r;
    in>>p;
    while(p)
    {
        for(i=1, r=1; r<=p; i*=5, r=r*5+1);
        r=(r-1)/5;
        n+=i*(p/r);
        p-=r*(p/r);
    }
    out<<n<<'\n';
    in.close(); out.close();
    return 0;
}