#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int p,n,nrz , putere;
    fin>>p;
    if(p==0)
    {
        fout<<1;
        return 0;
    }
    n=0;
    do  {
            n+=5;
            nrz = 0;
            putere = 5;
            while(n/putere>0)
                {
                    nrz+=n/putere;
                    putere *= 5;
                }
        }
    while(nrz<p);
    if(nrz==p)
        fout<<n;
        else if(nrz>p)
            fout<<-1;
    return 0;
}