Structural Mechanics

Consider the vector field v⃗ = - y r2 î + x r2 ĵ ; where r = √x2 + y2. The contour integral ∮ v⃗ ⋅ ds⃗⃗⃗⃗⃗, where ds⃗⃗⃗⃗⃗ is tangent to the contour that encloses the origin, is __________ (accurate to two decimal places).