#include <fstream>
using namespace std;

ifstream in ("factorial.in");
ofstream out ("factorial.out" );

int zero (int n)
{
    int nr=0;
    while (n>=5)
    {
        nr+=n/5;
        n/=5;
    }
    return nr;
}
int caut (int x)
{
    int i=0, pas=1<<30;
    while (pas!=0)
    {
        if (zero(i+pas)<x)
            i+=pas;
        pas/=2;
    }
    return 1+i;
}
int main()
{
    int p, n;
    in>>p;
    n=caut (p);
    if (zero(n)==p) out << n<<"\n";
    else out<<"-1\n";
    return 0;
}