#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long n,in,sf,rasp,mij,p,nr;
int main()
{
    f>>n;
    in=1;
    sf=5*n;
    rasp=-1;
    while(in<=sf)
    {
        mij=(in+sf)/2;
        p=5;
        nr=0;
        while(p<=mij)
        {
            nr=nr+mij/p;
            p=p*5;
        }
        if(nr<n)
        {
            in=mij+1;
        }
        else if(nr>n)sf=mij-1;
        else {rasp=mij-mij%5;break;}
    }
    if(n>0)g<<rasp;
    else g<<1;
    return 0;
}