hi,
  very simple you will get less diffusion cap... roughly i remember it will be half of the original cap provided if your fingers are very high
  there i assumed that gates of both m1 and m2 are connected, in that case m2 will be in triode and if both w1 and w2 are equal then m3 size will be w1/(l1+l2), if they are not equal then i guess very big equation will come.

thanks,
rajasekhar.