#include<iostream>
#include<fstream>
using namespace std;

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

int main(){
    int n,i,k=0,x;
    fin>>n;
    for(i=5;i<=n;i=i+5){
        x=i;
        while(x%5==0)k++;}
    fout << k;
    return 0;
}