#include<bits/stdc++.h>
using namespace std;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

template <typename T> using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

// macros
#define int long long 
#define ll long long 
#define ld long double
#define TIME clock() * 1.0 / CLOCKS_PER_SEC
#define sz(x) ((int)((x).size()))

template <typename A, typename B>
string to_string(pair<A, B> p);
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char& s) {
  return to_string(string(1, s));
}
 
string to_string(const char* s) {
  return to_string((string) s);
}
 
string to_string(bool b) {
  return (b ? "1" : "0");
}
 
string to_string(vector<bool> v) {
	bool first = true;
	string res = "{";
	for (int i = 0; i < static_cast<int>(v.size()); i++) {
		if (!first) {
			res += ", ";
		}
		first = false;
		res += to_string(v[i]);
	}
	res += "}";
	return res;
}
 
template <size_t N>
string to_string(bitset<N> v) {
	string res = "";
	for (size_t i = 0; i < N; i++) {
		res += static_cast<char>('0' + v[i]);
	}
	return res;
}
 
template <typename A>
string to_string(A v) {
	bool first = true;
	string res = "{";
	for (const auto &x : v) {
		if (!first) {
			res += ", ";
		}
		first = false;
		res += to_string(x);
	}
	res += "}";
	return res;
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
	return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
    return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
 
void debug_out() { cerr << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
 
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

template <typename T1, typename T2>
inline auto mini(T1 a, T2 b) { return (a < b ? a : b); }
template<typename T, typename... Args>
inline auto mini(T a, Args... args) { return mini(a, mini(args...)); }
template <typename T1, typename T2>
inline auto maxi(T1 a, T2 b) { return (a > b ? a : b); }
template<typename T, typename... Args>
inline auto maxi(T a, Args... args) { return maxi(a, maxi(args...)); }
template<typename T>
T gcd(T a, T b) { if(a==0 or b==0) return a+b; return gcd(b, a%b) ; }
template<typename T>
T lcm(T a, T b) { if(a==0 or b==0) return 0; return a/gcd(a, b)*b; }

// random number generator
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); // use mt19937_64 for 64 bit

// constants
const long double eps = LDBL_EPSILON;
const int inf = 1e15;
const int modn = 1e9+7;
const int maxn = 3e3+3;

int dp[maxn][maxn][4];

int32_t main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    // Your code here
	int n, m, k;
	cin >> n >> m >> k;
	vector<vector<int>> a(n, vector<int>(m));
	for(int i = 0 ; i < k; i++) {
		int r, c, v;
		cin >> r >> c >> v;
		r--, c--;
		a[r][c] = v;
	}	
	memset(dp, -1, sizeof(dp));
	function<int(int, int, int)> solve = [&](int i, int j, int taken) {
		assert(taken <= 3);
		if(i == n - 1 and j == m - 1) {
			if(taken == 3) {
				return 0LL;
			}
			return a[n - 1][m - 1];
		}

		int &ans = dp[i][j][taken];
		if(ans != -1) return ans;

		ans = 0;
		if(j != m - 1) {
			// go right
			int val = a[i][j];
			ans = max(ans, solve(i, j + 1, taken));
			if(val > 0 and taken < 3) {
				ans = max(ans, val + solve(i, j + 1, taken + 1));
			}
		}
		if(i != n - 1) {
			// go down
			int val = a[i][j];
			ans = max(ans, solve(i + 1, j, 0));
			if(taken < 3) {
				ans = max(ans, val + solve(i + 1, j, 0));
			}
		}
		return ans;
	};
	cout << solve(0, 0, 0) << "\n";
    return 0;
}

Measured memory_bytes: 356380