#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int p,st,dr,mid,nr,s;
int main()
{
    in>>p;
    if(p==0)
        out<<1;
    else
    {
        st=1;
        dr=5*p;
        while(st<=dr)
        {
            mid=(st+dr)/2;
            s=0;
            nr=5;
            while(nr<=mid)
            {
                s=s+mid/nr;
                nr=nr*5;
            }
            if(s==p)
            {
                out<<mid-mid%5;
                return 0;
            }
            else if(s<p)
                st=mid+1;
            else
                dr=mid-1;
        }
        out<<-1;
    }
}