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

# Initialize prefix sums for each character
prefix = [[[0]*(W+1) for _ in range(H+1)] for __ in range(26)]
for c in range(26):
    char = chr(ord('a') + c)
    for i in range(1, H+1):
        for j in range(1, W+1):
            current = 1 if grid[i-1][j-1] == char else 0
            prefix[c][i][j] = prefix[c][i-1][j] + prefix[c][i][j-1] - prefix[c][i-1][j-1] + current

count = 0
max_size = min(H, W)
for s in range(1, max_size + 1):
    for a in range(1, H - s + 2):
        for b in range(1, W - s + 2):
            a_end = a + s - 1
            b_end = b + s - 1
            unique = 0
            for c in range(26):
                if unique > K:
                    break
                total = prefix[c][a_end][b_end] - prefix[c][a-1][b_end] - prefix[c][a_end][b-1] + prefix[c][a-1][b-1]
                if total > 0:
                    unique += 1
            if unique == K:
                count += 1

print(count)