#include<bits/stdc++.h>
using namespace std;
//#define int long long
#define fi first
#define se second
#define pb push_back
#define mp make_pair
typedef pair<int, int> ii;
typedef pair<ii, int> iii;
typedef pair<ii, ii> iiii;
const int N = 3e3 + 5;
const int oo = 1e18 + 7, mod = 1e9 + 7;
int n, m;
long long val[N][N], pref[N][N];
// dp[row_i][row_j][i - 1 > or = or <]
long long dp[N][N][2];
long long 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++){
val[_x[i] + 1][_y[i] + 1] += (long long)_w[i];
}
for(int i = 1; i <= n; i++){
for(int j = 1; j <= n; j++) pref[i][j] = pref[i][j - 1] + val[i][j];
}
for(int i = 0; i <= n; i++){
for(int j = 0; j <= n; j++){
dp[i][j][0] = dp[i][j][1] = -oo;
}
}
//dp[0][0][0] = 0;
//15206896898496
for(int i = 0; i <= n; i++){
//dp[2][i][0] = pref[1][i];// 0 -> <=
//dp[2][i][1] = pref[2][i;
dp[1][i][0] = 0;
}
for(int i = 2; i <= n + 1; i++){
// calculate (i - 1)
long long maximum = -oo;
for(int nxt = 0; nxt <= n; nxt++){
maximum = max(maximum, dp[i - 1][nxt][0] - pref[i - 1][nxt]);
dp[i][nxt][0] = max(dp[i][nxt][0], maximum + pref[i - 1][nxt]);
}
maximum = -oo;
for(int nxt = n; nxt >= 0; nxt--){
dp[i][nxt][1] = max(dp[i][nxt][1], maximum - pref[i][nxt]);
maximum = max(maximum, dp[i - 1][nxt][1] + pref[i][nxt]);
}
for(int lst = 0; lst <= n; lst++){
// 0 - 0
/*
for(int nxt = lst; nxt <= n; nxt++){
dp[i][nxt][0] = max(dp[i][nxt][0], dp[i - 1][lst][0] + (pref[i - 1][nxt] - pref[i - 1][lst]));
}
// 1 - 1
for(int nxt = lst - 1; nxt >= 0; nxt--){
dp[i][nxt][1] = max(dp[i][nxt][1], dp[i - 1][lst][1] + pref[i][lst] - pref[i][nxt]);
}*/
// 0 - 1
if(lst == n){
for(int nxt = 0; nxt < n; nxt++) dp[i][nxt][1] = max(dp[i][nxt][1], dp[i - 1][n][0] + pref[i][n] - pref[i][nxt]);
}
// 1 - 0
if(!lst){
dp[i][0][0] = max(dp[i][0][0], dp[i - 1][0][1]);
for(int nxt = 1; nxt <= n; nxt++) dp[i][nxt][0] = max(dp[i][nxt][0], max(dp[i - 1][0][0] + pref[i - 1][nxt], dp[i - 1][0][1]));
}
}
}
return max(dp[n + 1][0][0], dp[n + 1][0][1]);
}
/*
void process(){
int n, m;
vector<int> a, b, c;
cin >> n >> m;
for(int i = 1; i <= m; i++){
int x, y, z;
cin >> x >> y >> z;
a.pb(x), b.pb(y), c.pb(z);
}
cout << max_weights(n, m, a, b, c) << "\n";
}
signed main(){
ios_base::sync_with_stdio(0);
freopen("fish.inp", "r", stdin);
//freopen("fish.out", "w", stdout);
//cout << "OK\n";
//return 0;
process();
}*/
