//fact INFOARENA

#include <fstream>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

unsigned long long nrcifre(unsigned long long a){
    unsigned long long cifre=0;
    while (a>0)
    {
        cifre+=a/5;
        a/=5;
    }
    return cifre;

}
unsigned long long cautare(unsigned long long p)
{
    unsigned long long c,n=0,st,sf,mij,r1,r2,stf,sff;
    st=1;
    sf=n=1<<31;
    while (st<=sf)
    {   
	r1=st%2;
	r2=sf%2;
	stf=st/2;
	sff=sf/2;
	mij=stf+sff+(r1+r2)/2;
        if (nrcifre(mij)>=p){
            if (mij<n) n=mij;
            sf=mij-1;
        } else
        {
            st=mij+1;
        }
    }
    return n;


}
int main()
{
    unsigned long long p;
    fin>>p;
    fout<<cautare(p);
    fout.close();
    return 0;
}