#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{
    int n, x, s=0;
    f>>n;
    if (n==0) g<<1;
    else if (n==1) g<<0;
    else{
    x=n;
    while (x%5 == 0) {
        s++;
        x/=5;
    }
    while (n%25 == 0) {
        s--;
        x/=25;
    }
    g<<s*5;
    return 0;
}}