var i,x,m,p,c,s,ok1,ok2:longint; f1,f2:text;

procedure putere(x:longint);
begin
        p:=1;
        s:=0;
        while p*5<=x do
        begin
                p:=p*5;
                s:=s+x div p;
        end;
end;

procedure search(li,ls:longint);
begin
        m:=(li+ls) div 2;
        putere(m);
        ok1:=s;
        putere(m-1);
        ok2:=s;
        if (ok1=x)and(ok2<x) then c:=m
                else if li<ls then
                        if ok2>=x then search(li,m-1)
                                 else search(m+1,ls);
end;

begin
        assign(f1,'fact.in');
        reset(f1);
        assign(f2,'fact.out');
        rewrite(f2);
        read(f1,x);
        search(1,maxlongint);
        if c=0 then dec(c);
        writeln(f2,c);
        close(f1);
        close(f2);
end.