#include "fish.h"
#include<bits/stdc++.h>
using namespace std;
using lint=long long;
const int lim=3e3+100;
int n,m;
lint dp[lim][lim],up[lim][lim];
lint pref[lim][lim];
lint p(int i,int l,int r){
if(r<l)return 0;
if(l){
//cerr<<pref[i][r]<<" "<<pref[i][l-1]<<" "<<pref[i][r]-pref[i][l-1]<<"\n";
return pref[i][r]-pref[i][l-1];
}
return pref[i][r];
}
lint max_weights(int N, int M, std::vector<int> X, std::vector<int> Y,
std::vector<int> W) {
n=N,m=M;
for(int i=0;i<m;i++){
pref[X[i]][Y[i]+1]+=W[i];
}
for(int i=0;i<=n;i++){
for(int j=1;j<=n;j++){
pref[i][j]+=pref[i][j-1];
}
}
n=N,m=M;
for(int i=0;i<=n;i++){
dp[0][i]=p(1,0,i);
//cerr<<dp[0][i]<<" ";
}//cerr<<"\n\n";
for(int i=1;i<n;i++){
lint max1=0;
for(int j=0;j<=n;j++){
max1=max(max1,up[i-1][j]-pref[i-1][j]);
dp[i][j]=max(dp[i][j],max1+pref[i-1][j]+p(i+1,0,j));
up[i][j]=max(up[i][j],max1+pref[i-1][j]);
up[i][j]=max(up[i][j],dp[i-1][j]);
}
max1=0;
for(int j=n;0<=j;j--){
max1=max(max1,dp[i-1][j]);
dp[i][j]=max(dp[i][j],max1-p(i,0,j)+p(i+1,0,j));
}
/*
for(int j=0;j<=n;j++){
cerr<<dp[i][j]<<" ";
}cerr<<"\n";
for(int j=0;j<=n;j++){
cerr<<up[i][j]<<" ";
}cerr<<"\n\n";
*/
}
lint ans=0;
for(int i=0;i<=n;i++){
ans=max(ans,dp[n-1][i]);
}
return ans;
}
