#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=1000000000, min=1, x, m;
    fin>>p;
    if (p==0) 
	{
		fout<<"1\n";
		return 0;
	}
	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(x)==p) 
    {
       while (f(x-1)==p)
          x--;
       fout<<x;
    }
        else fout<<"-1";
    return 0;
}