import sys

def main():
    H, W, K = map(int, sys.stdin.readline().split())
    grid = [sys.stdin.readline().strip() for _ in range(H)]
    ans = 0

    for s in range(1, min(H, W) + 1):
        if s > H or s > W:
            continue
        # Precompute the bitmask for each column's sliding window of s rows
        masks = [0] * W
        for j in range(W):
            mask = 0
            for i in range(s):
                mask |= 1 << (ord(grid[i][j]) - ord('a'))
            masks[j] = mask
        
        for i in range(H - s + 1):
            current_or = 0
            count = 0
            # Initialize the first s columns
            for j in range(s):
                current_or |= masks[j]
            if bin(current_or).count('1') == K:
                count += 1
            
            # Slide the window across columns
            for j in range(1, W - s + 1):
                # Remove the leftmost column
                left = j - 1
                # Add the new rightmost column
                right = j + s - 1
                # Recompute current_or as the OR of the s columns in the current window
                current_or = 0
                for k in range(j, j + s):
                    current_or |= masks[k]
                if bin(current_or).count('1') == K:
                    count += 1
            ans += count

            # Update masks for next row
            if i < H - s:
                for j in range(W):
                    # Remove the top character and add the new bottom character
                    top_char = grid[i][j]
                    bottom_char = grid[i + s][j]
                    if top_char == bottom_char:
                        continue  # Mask remains the same
                    # Recompute the mask for this column
                    new_mask = 0
                    for k in range(i + 1, i + 1 + s):
                        new_mask |= 1 << (ord(grid[k][j]) - ord('a'))
                    masks[j] = new_mask

    print(ans)

if __name__ == "__main__":
    main()