var f,g:text;
    i,n,p,k,m:int64;
begin
        assign(f,'fact.in');
        reset(f);
        readln(f,p);
        close(f);

        n:=1;
        i:=1;
        k:=0;
        while (k<p)and(n<9000000000000000000) do begin
                m:=n;
                k:=0;
                repeat
                        if m mod 10 =0 then inc(k)
                                else
                                        m:=0;
                        m:=m div 10;
                until m=0;
                inc(i);
                n:=n*i;
                end;
       assign(g,'fact.out');
       rewrite(g);
       writeln(g,i);
       close(g);
end.