#include <fstream>
using namespace std;

fstream f("fact.in" ,ios::in), g("fact.out", ios::out);

int main()
{
    unsigned long long p,nr,aux,t;
    f>>p;
    if(p==1)
        g<<"0";
    else
    {
        nr=5;
        t=1;
        while (t<p)
        {
            nr+=5;
            aux=nr;
            while (aux%5==0)
            {
                aux/=5;
                t++;
            }
        }
        g<<nr;
    }
    return 0;
}