am... i used partial derivate so i got:

df/dx = 3x^2 - 3y

df/dy = 3y^2 - 3x

local ekstrems are:

3x^2 - 3y = 0

3y^2 - 3x = 0

.

.

.

x1 = 0, x2 = 1

y1 = 0, y2 = 1

and then, where is maximum and where is "saddle",... I did secodn derivate and I used Hessian matrix, so in point (0,0) this matrix is negative (-9, so this is saddle right? - is this minimum?) and in point (1,1) a got positive matrix (27 - is this maximum or what?). Is all correct or I did some mistakes?