#include<fstream>
using namespace std;
 
long long f(long long x)
{
    int p=5,nr=0;
    while (p<=x)
    {
        nr=nr+x/p;
        p=p*5;
    }
    return nr;
}
 
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    long long p, max=100000000, min=0, x, m;
    fin>>p;
    if (p==0) min=1;
        else while (min<max)
            {
                x=(min+max)/2;
                m=f(x);
		if (m==p) break;
                if (m<p) min=x+1;
                    else max=x;
            }       
    if (f(min)==p) 
    {
       while (f(min-1)==p)
          min--;
       fout<<min;
    }
        else fout<<"-1";
    return 0;
}