H, W, K = map(int, input().split())
grid = [input().strip() for _ in range(H)]

count = 0

for a in range(H):
    for b in range(W):
        charset = set()
        max_s = min(H - a, W - b)
        for s in range(1, max_s + 1):
            # Add new row (a + s - 1) from column b to b + s - 1
            new_row = a + s - 1
            for j in range(b, b + s):
                c = grid[new_row][j]
                if c not in charset:
                    charset.add(c)
            # Add new column (b + s - 1) from row a to a + s - 2 (excluding the last cell)
            new_col = b + s - 1
            for i in range(a, a + s - 1):
                c = grid[i][new_col]
                if c not in charset:
                    charset.add(c)
            # Check current count
            current = len(charset)
            if current == K:
                count += 1
            elif current > K:
                break  # Further expansion won't reduce the count

print(count)