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

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int c,i,d,n;
    f>>n;
    for(i=1;i<=n;i++){
                        if(i%2==0){
                                  d=d+i/2;
                                   }
                         if(i%5==0){
                                   c=c+i/5;
                                   }


                     }
    g<<min(d,c);
    f.close();
    g.close();
    return 0;
}