#include <fstream>

using namespace std;

long long int n,mij,s,d,p,rasp;
int v[18]={0,5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140725,1220703125};

int main()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    fin>>p;
    n=-1;
    if (p>=1)
    {
        s=1,d=p*5;
        mij=(s+d)/2;
        rasp=0;
        for (int i=1;v[i]<=mij;++i)
        {
            rasp+=mij/v[i];
        }
        if (rasp==p)
        {
            n=mij;
            d=mij-1;
        }
        else
        {
            if (rasp<p)
            {
                s=mij+1;
            }
            else
            {
                d=mij-1;
            }
        }
        fout<<n;
    }
    fout<<"1";
}