  We study the minimal number C(M,\xi) of contact charts that one needs to
cover a closed connected contact manifold (M,\xi). Our basic result is C(M,\xi)
\le \dim M + 1.
  We compute C(M,\xi) for all closed connected contact 3-manifolds:
  C (M,\xi) = 2 if M = S^3 and \xi is tight,
  3 if M = S^3 and \xi is overtwisted or if M = #_k (S^2 \times S^1),
  4 otherwise.
  We also show that on every sphere S^{2n+1} there exists a contact structure
with C(S^{2n+1},\xi) \ge 3.
