#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    long long P,s=0,j;
    fin>>P;
    if(!P)fout<<1;
    else{
        for(int i=5;i<=P;i+=5)
            {   j=i;
                while(j%5==0)
                {
                    s++;
                    j/=5;
                }
            }
        fout<<s;
    }
    return 0;
}