  We compute celestial amplitudes corresponding to the exact S-matrix of the 2d
O(N)-symmetric nonlinear sigma model. Celestial amplitudes for two-dimensional
integrable S-matrices simplify to Fourier transforms. Due to the connection
between Fourier and Mellin transforms, celestial amplitudes for O(N) model are
Mejer G-functions. We also prove crossing symmetry for obtained results and
review simplifications for O(3) symmetry case.
