Consider a prismatic straight beam of length L = π m, pinned at the two ends as shown i n t he figure. The beam has a square cross-section of side p = 6 mm. The Young's modulus E = 20 GPa, and the coefficient of thermal expansion α = 3 × 10^{– 6} K ^{– 1}. The minimum temperature rise required to cause Euler buckling of the beam is ______ K.