The expressions A=1 \times 2+3 \times 4+5 \times 6+\cdots+37 \times 38+39 and B= 1+2 \times 3+4 \times 5+\cdots+36 \times 37+38 \times 39 are obtained by writing multiplication and addition operators in an alternating pattern between successive integers. Find the positive difference between integers A and B.