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

int main()
{
long d,a,b,c,N,p,q,i,j,l,numar,mota;

ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
d=0;
a=1;
l=0;
q=0;
numar=0;
while(numar!=p)
{ mota=a;
c=a;
   while(mota%2==0)
   { l=l+1;
       mota=mota/2;
   }
    while(c%5==0)
    {
        q=q+1;
        c=c/5;
    }
   if(l>q)
   {
       numar=numar+q;
q=0;
l=l-q;
   }
if(q>l)
{
    numar=numar+l;
    l=0;
    q=q-l;
}

if(q==l)
{
    numar=numar+q;
    q=0;
    l=0;
}

a=a+1;
}
g<<a-1;
     return 0;
}