#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long nrz,n,m,nrz1;

void prelucrare()
{
    n = nrz*4;
    while(nrz1 < nrz)
    {
        nrz1 = 0;
        m = n;
        while(m != 0)
            m /= 5,nrz1 = nrz1 + m;
        n++;
    }
}
long long afisare()
{

    if(nrz1 != nrz)
        return -1;
    else if(nrz == 0)
        return 1;
    else
        return n-1;
}
int main()
{
    f >> nrz;
    prelucrare();
    g << afisare();
    return 0;
}