为什么RE了一个点....

#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll n,m=-0x7fffffff/2,ans,cnt;
ll dp[1000005]={0},h[1000005];
struct Way{ll Start,End,sum;}way[1000005];
struct EDGE{ll next,to;}e[1000005];
void add(ll x,ll y)
{
	cnt++;
	e[cnt].to=y;
	e[cnt].next=h[x];
	h[x]=cnt;
}
void Get_DP()
{
	ll i,j;
	for(i=1;i<=m;i++)
	{
		dp[i]=dp[i-1];
		if(h[i])
		for(j=h[i];j;j=e[j].next)
		dp[i]=max(dp[i],dp[i-e[j].to]+e[j].to);
	}
	ans=dp[m];
}
void judge()
{
	ll i,j;
	for(i=1;i<=m;i++)cout<<dp[i]<<" ";
}
int main()
{
	ll i,j;
	cin>>n;
	for(i=1;i<=n;i++)
	{
		cin>>way[i].Start>>way[i].End;
		way[i].sum=way[i].End-way[i].Start+1;
		add(way[i].End,way[i].sum);
		m=max(m,way[i].End);
	}
	Get_DP();
	//judge();
	cout<<ans;
	return 0;
}