为啥初始化不是都为-1e9，而是这样

#include<bits/stdc++.h>
using namespace std;
struct as{
	int x,y;
}; 
as a[3005];
bool cmp(as g,as h){
	return g.x>h.x;
}
int dp[3005][3005];
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i].x>>a[i].y;
	}
	sort(a+1,a+n+1,cmp);
	for(int i=0;i<=n;i++){
		dp[0][i]=-1e9;
		dp[i][n+1]=-1e9;
	}
	dp[0][1]=0;
	int ma=-1000000000;
	for(int i=1;i<=n;i++){
		for(int j=0;j<=n;j++){
			dp[i][j]=max(dp[i-1][j],dp[i-1][max(j-a[i].x,0)+1]+a[i].y);
			ma=max(ma,dp[i][j]);
		}
	}
	cout<<ma;
	return 0;
}