#include <iostream>
#include <fstream>
using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
long long n,p,ls,ld;
int nz (int n)
{
    int k=n,p=5;
    while (p<=n)
    {
        k+=n/p;
        p=p*5;
    }
    return k;
}

int main()
{
    int h;
    f>>p;
    if (p!=0)
    {
        ls=1;
        ld=1000000000;
        int sw=0;
        while (ls<=ld&&!sw)
        {
            h=nz((ls+ld)/2);
            if (p>h&&p<nz((ls+ld)/2+1))
            {
                sw=1;
                g<<(ls+ld)/2*5+5;
            }
            else if (p>h) ls=(ls+ld)/2+1;
            else if (p<h) ld=(ls+ld)/2-1;
            else
            {
                g<<((ls+ld)/2)*5;
                sw=1;
            }
        }
    }
    else g<<1;
    return 0;
}