Trouble in writing equation

I am trying to create a function for following equation but getting no luck.

I tried the following code but i dont know its correct or not.Kindly help me

function [obj2] = Calculateangle(x,y)
 
for i=0:N
   brg= atan2(y(i+1)-y(i))/(x(i+1)-x(i));
   brg2= atan2(y(N+1)-y(i))/(x(N+1)-x(i));
end
      obj2=brg-brg2
end