#include <bits/stdc++.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int numar,n,x;
int main()
{
           f>>n;
            int i=0;
            while(numar!=n)
            {
                i++;
                x=i;
                while(x%5==0)
                {numar++;
                x=x/5;
                }
            }
            g<<i;
}