#include <bits/stdc++.h>
using namespace std;
const int32_t N = 1e5 + 5,
M = 3e5 + 5;
const int64_t INF = 1e18;
int n, m;
struct info{
int x, y, w;
info(){}
info(int x, int y, int w): x(x), y(y), w(w) {}
} fish[M];
namespace sub1{
long long solve(){
long long res = 0LL;
for(int i = 1; i <= m; i++) res += fish[i].w;
return res;
}
}
namespace sub6{
long long dp[3005][3005][2], weight[3005][3005], pref1[3005][3005], pref2[3005][3005], pref3[3005];
long long solve(){
for(int i = 1; i <= m; i++) weight[fish[i].x][fish[i].y] = fish[i].w;
long long res = 0;
for(int i = 1; i <= n; i++){
if(i > 0) pref3[i] = -INF;
for(int j = 0; j <= n + 1; j++){
for(int z = 0; z <= 1; z++) dp[i][j][z] = max(dp[i][j][z], dp[i - 1][j][z]);
if(i > 1) pref1[i][j] = -INF;
pref2[i][j] = -INF;
}
if(i > 1){ // case 0
long long add = 0, sub = 0;
for(int j = 1; j <= n; j++){
add += weight[i][j];
sub += weight[i - 1][j];
dp[i][j][0] = max(dp[i][j][0], pref1[i - 1][j] + add - sub);
}
for(int j = 1; j <= n; j++) dp[i][n][0] = max({dp[i][n][0], dp[i - 2][j][0] + add, dp[i - 2][j][1] + add});
for(int j = n; j >= 1; j--) pref1[i][j] = max(pref1[i][j + 1], dp[i][j][0]);
res = max(res, pref1[i][1]);
}
if(i < n){
long long add = 0;
for(int j = 1; j <= n; j++){
add += weight[i][j];
dp[i][j][1] = max(dp[i][j][1], pref2[i - 1][j] + add);
}
add = 0;
for(int j = 1; j <= n; j++){
add += weight[i + 1][j];
pref2[i][j] = max(pref2[i][j - 1], dp[i][j][1] - add);
pref3[i] = max(pref3[i], dp[i][j][1]);
}
add = 0;
for(int j = 1; j <= n; j++){
add += weight[i][j];
dp[i][j][1] = max(dp[i][j][1], pref1[i - 1][1] + add);
if(j >= 2) dp[i][j][1] = max(dp[i][j][1], pref3[i - 2]);
}
res = max(res, dp[i][n][1]);
}
}
return res;
}
}
int64_t max_weights(int _N, int _M, vector<int> _X, vector<int> _Y, vector<int> _W){
n = _N; m = _M;
for(int i = 0; i < m; i++) fish[i + 1] = info(_X[i] + 1, _Y[i] + 1, _W[i]);
bool flag1 = true;
for(int i = 1; i <= m; i++) if(!(fish[i].x & 1)){ flag1 = false; break; }
if(flag1) return sub1::solve();
else return sub6::solve();
}
//#define zNatsumi
#ifdef zNatsumi
int main(){
cin.tie(0)->sync_with_stdio(0);
#define task "test"
if(fopen(task ".inp", "r")){
freopen(task ".inp", "r", stdin);
freopen(task ".out", "w", stdout);
}
int n, m; cin >> n >> m;
vector<int> x(m), y(m), w(m);
for(int i = 0; i < m; i++) cin >> x[i] >> y[i] >> w[i];
cout << max_weights(n, m, x, y, w);
}
#endif
