Basically using Euler's formula, V-E+F=1, where F=2005.
Besides the four corners, every vertex is of degree at least 3, so we have 8+3(V-4) ≤ 2E. Combine these two, we get the answer.
Besides the four corners, every vertex is of degree at least 3, so we have 8+3(V-4) ≤ 2E. Combine these two, we get the answer.