#pragma GCC optimize("Ofast") 
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define mp make_pair                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define MOD (ll)(998244353)
#define INF (ll)(1e18)
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
int gcd(int A,int B) {if(!B)return A;return gcd(B,A%B);}
ll dp[4][3000][3000];
int main()
{
  owo
	int r,c,k;
	cin>>r>>c>>k;
	VII grid(r,vector<ll>(c,0));
	for(int i=0;i<r;i++){
		for(int j=0;j<c;j++){
			dp[0][i][j] = dp[1][i][j] = dp[2][i][j] = dp[3][i][j] = -INF;
		}
	}
	for(int i=0;i<k;i++){
		ll x,y,v;
		cin>>x>>y>>v;
		x--;y--;
		grid[x][y] = v;
	}
	dp[0][0][0] = 0;
	if(grid[0][0])dp[1][0][0] = grid[0][0];
	for(int i=0;i<r;i++){
		for(int j=0;j<c;j++){
			   for(int l=0;l<4;l++){
				   if(i)dp[0][i][j] = max(dp[l][i-1][j],dp[0][i][j]);//take nothing
				   if(j)dp[l][i][j] = max(dp[l][i][j-1],dp[l][i][j]);
			   }
			   if(grid[i][j] > 0){
				   for(int l=0;l<4;l++){
					   if(i && dp[l][i-1][j] >=0){
						   dp[1][i][j] = max(dp[1][i][j],dp[l][i-1][j]+grid[i][j]);
					   }
				   }
				   for(int l=1;l<4;l++){
					   if(j && dp[l-1][i][j-1] != INF){
						   dp[l][i][j] = max(dp[l][i][j],dp[l-1][i][j-1]+grid[i][j]);
					   }
				   }
			   }
		}
	}
	ll ans = 0;
	for(int i=0;i<4;i++)ans=max(ans,dp[i][r-1][c-1]);
	cout<<ans;
}


Measured memory_bytes: 354784