import sys

def main():
    H, W, K = map(int, sys.stdin.readline().split())
    grid = [sys.stdin.readline().strip() for _ in range(H)]
    
    # Precompute prefix sums for each character
    prefix = {}
    for c in 'abcdefghijklmnopqrstuvwxyz':
        pre = [[0]*(W+1) for _ in range(H+1)]
        for i in range(1, H+1):
            row = [0]*(W+1)
            for j in range(1, W+1):
                row[j] = row[j-1] + (1 if grid[i-1][j-1] == c else 0)
                pre[i][j] = pre[i-1][j] + row[j]
        prefix[c] = pre
    
    result = 0
    max_s = min(H, W)
    for s in range(1, max_s+1):
        for a in range(1, H - s + 2):
            for b in range(1, W - s + 2):
                x1, y1 = a, b
                x2, y2 = a + s - 1, b + s - 1
                distinct = 0
                for c in 'abcdefghijklmnopqrstuvwxyz':
                    sum_c = prefix[c][x2][y2] - prefix[c][x1-1][y2] - prefix[c][x2][y1-1] + prefix[c][x1-1][y1-1]
                    if sum_c > 0:
                        distinct += 1
                if distinct == K:
                    result += 1
    print(result)

if __name__ == "__main__":
    main()