import sys
from collections import defaultdict

def main():
    H, W, N = map(int, sys.stdin.readline().split())
    C = []
    for _ in range(H):
        row = list(map(int, sys.stdin.readline().split()))
        C.append(row)
    
    adj = defaultdict(set)
    for i in range(H):
        for j in range(W):
            current = C[i][j]
            for dx, dy in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
                ni, nj = i + dx, j + dy
                if 0 <= ni < H and 0 <= nj < W:
                    neighbor = C[ni][nj]
                    if current != neighbor:
                        adj[current].add(neighbor)
                        adj[neighbor].add(current)
    
    max_color = 0
    d = [0] * (N + 1)  # d[1..N]
    for k in range(1, N + 1):
        current_max_neighbor = 0
        for neighbor in adj.get(k, set()):
            if neighbor < k:
                if d[neighbor] > current_max_neighbor:
                    current_max_neighbor = d[neighbor]
        current_d = max(max_color, current_max_neighbor + 1)
        d[k] = current_d
        if current_d > max_color:
            max_color = current_d
    print(max_color)

if __name__ == "__main__":
    main()