#include <iostream>
#include <time.h>

using namespace std;

int nz(int);

int main()
{
    int n;
    cin>>n;
    cout<<nz(n);
    return 0;
}

int nz(int n){
    int i,j,nr=0,k,sum=1;
    clock_t ceas;
    ceas=clock();
    for(i=1;i<=n;i++){
        if(i%5==0){
            k=i;
            while(k%5==0){
                nr++;
                k=k/5;
            }
        }
    }
    cout<<clock()-ceas<<endl;
    return nr;
}