The contour of this integration is a square form by (1,i),(1,-i),(-1,i),(-1,-i)
How to show that $\int_c dz/z$ = $2\pi i$ without deformation of contour or parametize by $z=e^{it}$?
i 've try to use the formula \int_c f(z)dz=\int ^b _a f(z(t))z'(t)dt but everything doesn't seems too neat!