var xoa binary;
var xob binary;
var xoc binary;
var xab binary;
var xat binary;
var xbc binary;
var xbt binary;
var xca binary;
var xct binary;

minimize fointerv:	 30*xoa +  3*xob + 19*xoc + 
					 30*xab + 55*xat + 30*xbc + 
					102*xbt + 39*xca + 30*xct;

s.t. balance_o: xoa + xob + xoc = 1;
s.t. balance_t: xat + xbt + xct = 1;
s.t. balance_c: xoc + xbc - (xca + xct) = 0;
s.t. balance_b: xob + xab - (xbc + xbt) = 0;
s.t. balance_a: xoa + xca - (xab + xat) = 0;