import sys

def main():
    H, W, K = map(int, sys.stdin.readline().split())
    grid = []
    for _ in range(H):
        line = sys.stdin.readline().strip()
        row = [1 << (ord(c) - ord('a')) for c in line]
        grid.append(row)
    
    total = 0
    max_size = min(H, W)
    
    for s in range(1, max_size + 1):
        valid_width = W - s + 1
        if valid_width <= 0:
            continue
        temp = []
        for i in range(H):
            row = grid[i]
            temp_row = []
            for j in range(valid_width):
                or_val = 0
                for k in range(s):
                    or_val |= row[j + k]
                temp_row.append(or_val)
            temp.append(temp_row)
        
        valid_height = H - s + 1
        if valid_height <= 0:
            continue
        
        for j in range(len(temp[0])):
            for i in range(valid_height):
                or_val = 0
                for k in range(s):
                    or_val |= temp[i + k][j]
                cnt = bin(or_val).count('1')
                if cnt == K:
                    total += 1
    
    print(total)

if __name__ == "__main__":
    main()