#include <fstream>

using namespace std;
ifstream cin ("fact.in");
ofstream cout ("fact.out");
int main()
{
    long long n,y,x,p,cm,nr,m,st,dr,ok=0;
    cin>>p;
    st=1;
    dr=2000000000;
    while (st<=dr)
    {
        m=st+dr;
        m/=2;
        cm=5;
        nr=0;
        while (cm<=m)
        {
            nr=nr+m/cm;
            cm*=5;
        }
        if (nr<p)
            st=m+1;
        else
        if (nr>=p)
        {
            x=m;
            dr=m-1;
            y=nr;
        }
    }
    if (y==p)
    cout<<x;
    else
    cout<<-1;
    return 0;
}