H, W, X = map(int, input().split())

if H % 4 == 3 and W % 4 == 3:
    if X == H + W - 2:
        for i in range(H):
            for j in range(W):
                if i == 0 or j == W - 1:
                    print(".", end = "")
                else:
                    print("#", end = "")
            print("")
    else:
        print(-1)
    exit()

sw = False
if H % 4 == 3:
    W, H = H, W
    sw = True
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
minX = W + H - 2
if X > maxX or X < minX:
    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] = "."
if sw:
    for j in range(W):
        for i in range(H):
            print(ans[i][j], end = "")
        print("")
else:
    for i in range(H):
        print("".join(ans[i]))