H, W, X = map(int, input().split())
ans = [["."] * W for i in range(H)]
for i in range(H):
    for j in range(W):
        if i % 2 == 1:
            ans[i][j] = "#"
maxX = (W * H + W + H - 3) // 2
if X > maxX:
    print(-1)
    exit()
if (maxX - X) % 4 != 0:
    print(-1)
    exit()
K = (maxX - X) // 4
L = True
for i in range(1, H, 2):
    L = not L
    k = min((W // 2), K)
    K -= k
    if L:
        ans[i][2 * k] = "."
    else:
        ans[i][W - 1 - 2 * k] = "."
for i in range(H):
    print("".join(ans[i]))