#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int nz(int n){
    int z=0;
    for(int i=1;i<=n;i++)
    {
        int k=i;
        while(k%5==0){
            z++;
            k=k/5;
        }
    }
    return z;
}
int main()
{
    int n;
    in>>n;
    out<<nz(n);
    return 0;
}