#include <iostream>
#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{

    int zf, zero=0;
    f >> zf;
    for(int a=0;; a+=5)
    {
        zero=0;
        for(int put5=5; put5<=a; put5*=5)
        zero+=a/put5;
        if(zero==zf)
        {
        g << a;
        break;
        }
    }







    return 0;
}