【CEOI2004】锯木厂选址(斜率优化入门题)

感谢QT神犇的技术支持！
斜率优化不想发，这是n^2算法+决策性优化，容易被卡。

#include<cstdio>
#include<cstdlib>
#include<ctime>
#include<iostream>
#include<cstring>
#include<algorithm> 
#define LL long long
#define INF 999999
using namespace std;
LL n,d;
LL w[2001000],dis[2001000],sw[2001000],val[2001000];
int main()
{
	scanf("%lld",&n);
	for(int i=1;i<=n;i++)
	{
		scanf("%lld%lld",&w[i],&d);
		val[i]=val[i-1]+w[i];
		sw[i]=sw[i-1]+dis[i]*w[i]; 
		dis[i+1]=dis[i]+d;
	}
//	for(int i=1;i<=n;i++) cout<<dis[i]<<" "<<val[i]<<' '<<sw[i]<<endl;
	LL last=2,ans=999999999;
	for(LL i=1;i<=n;i++)
	 for(LL j=last;j<=n;j++)
	{
		LL ans1=(dis[i]*val[i])-sw[i];
		LL ans2=dis[j]*(val[j]-val[i])-(sw[j]-sw[i]);
		LL ans3=dis[n+1]*(val[n]-val[j])-(sw[n]-sw[j]);
		if(ans>ans1+ans2+ans3) ans=ans1+ans2+ans3,last=j;
	}
	printf("%lld\n",ans);
	return 0;
}