A person $X$ wants to distribute some pens among six children $A$ , $B$ , $C$ , $D$ , $E$ and $F$ . Suppose $A$ gets twice the number of pens received by $B$ , three times that of $C$ , four times that of $D$ , five times that of $E$ and six times that of $F$ . What is the minimum number of pens $X$ should buy so that the number of pens each one gets is an even number?