h, w, x = map(int, input().split())
r = x - (h - 1) - (w - 1)
if r < 0 or r % 4:
    print(-1)
    exit()
r //= 4
s = [[(i | j) & 1 for j in range(w)] for i in range(h)]
for i in range(h):
    s[i][0] = 0
for j in range(w):
    s[h-1][j] = 0

di = [1, 0, -1, 0]
dj = [0, 1, 0, -1]
def flip(i, j):
    for k in range(4):
        ni = i + di[k]
        nj = j + dj[k]
        s[ni][nj] ^= 1
i = h - 2
j = w - 2
if j == 1:
    i -= 2

while r and i > 0 and j > 0:
    r -= 1
    flip(i, j)
    if j == 1:
        i -= 4
    else:
        i -= 2
    if i < 0:
        j -= 4
        i = h - 2
        if j == 1:
            i -= 2

if r != 0:
    print(-1)
    exit()
for si in s:
    print(''.join('.#'[x] for x in si))