此题有点让我无法形容

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int const xn=50005;
int n,h[xn],v[xn],sta[xn],top,s[xn];
int rd()
{
  int ret=0,f=1; char ch=getchar();
  while(ch<'0'||ch>'9'){if(ch=='-')f=0; ch=getchar();}
  while(ch>='0'&&ch<='9')ret=(ret<<3)+(ret<<1)+ch-'0',ch=getchar();
  return f?ret:-ret;
}
int main()
{
  n=rd();
  for(int i=1;i<=n;i++)
    {
      h[i]=rd(),v[i]=rd();
      while(top&&h[sta[top]]<=h[i])top--;
      if(top)s[sta[top]]+=v[i];
      sta[++top]=i;
    }
  top=0;
  for(int i=n;i;i--)
    {
      while(top&&h[sta[top]]<=h[i])top--;
      if(top)s[sta[top]]+=v[i];
      sta[++top]=i;
    }
  int mx=0;
  for(int i=1;i<=n;i++)mx=max(mx,s[i]);
  printf("%d\n",mx);
  return 0;
}