#include <fstream>
using namespace std;
int p;
int zerouri(int n)
{
    int pt5=5,suma=0;
    while(n/pt5)
    {
        suma=suma+n/pt5;
        pt5=pt5*5;
    }
    return suma;

}
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int stanga=1,dreapta=5*100000000;
    f>>p;
    while(stanga<=dreapta)
    {
        int mijloc=(stanga+dreapta)/2;
        if(zerouri(mijloc)<p)
            stanga=stanga+1;
        else
            dreapta=mijloc-1;
    }
    if(zerouri(stanga)==p)
        g<<stanga;
    else
       g<<-1;
    return 0;
}