#include <iostream>
#include <vector>
#include <algorithm>
#include <atcoder/string>
#include <atcoder/segtree>
using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(n); i++)

int H,W,N;
vector<vector<int>> G;
vector<vector<int>> E;
vector<int> D;

int main(){
  cin >> H >> W >> N;
  G.assign(H,vector<int>(W));
  rep(y,H) rep(x,W){ cin >> G[y][x]; G[y][x]--; }
  E.resize(N);
  rep(y,H) rep(x,W-1) if(G[y][x] != G[y][x+1]) E[min(G[y][x],G[y][x+1])].push_back(max(G[y][x],G[y][x+1]));
  rep(y,H-1) rep(x,W) if(G[y][x] != G[y+1][x]) E[min(G[y][x],G[y+1][x])].push_back(max(G[y][x],G[y+1][x]));
  D.assign(N+1,1);
  rep(i,N){
    for(int e : E[i]) D[e] = max(D[e], D[i] + 1);
    D[i+1] = max(D[i+1], D[i]);
  }
  cout << D.back() << endl;
  return 0;
}

struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_instance;