1-2/3-2/15-2/35-2/63-2/99-2/143
=1-(1-1/3)-(1/3-1/5)-(1/5-1/7)-(1/7-1/9)...-(1/11-1/13)
=1-1+1/3-1/3+1/5-1/5+1/7-1/7+1/9...-1/11+1/13
=1/13