#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int nrz(int n)
{
    int nr=0,i;

    for(i=5;i<=n;i=i*5)
        nr=nr+n/i;

    return nr;
}

int main()
{
    int st,dr,p,m;

    fin>>p;

    st=1;
    dr=5*p;

    while(st<=dr)
    {
        m=(dr+st)/2;

        if(nrz(m)>=p)
            dr=m-1;
        else
            st=m+1;
    }

    if(nrz(st)==p)
        fout<<st;
    else
        fout<<-1;


    return 0;
}