边界处理就是折磨王

#include<iostream>
#include<algorithm>

using namespace std;
const int N=1000005;
int a[N];
int main()
{

    int n;cin>>n;
    for(int i=1;i<=n;i++)
    cin>>a[i];
    long long m,s,p,q;
    cin>>m>>s>>p>>q;
    a[s]+=p;
    long long sum=0;
    for(int i=1;i<=n;i++)
     sum+=(m-i)*a[i];

   if(sum>0)
   {

       if(abs(sum-sum/q*q)>abs(sum-(sum/q+1)*q))
       cout<<m+sum/q+1<<endl;
       else
       cout<<m+sum/q<<endl;
   }
   else
   {
       if(abs(sum-sum/q*q)>=abs(sum-(sum/q-1)*q))
       cout<<m+sum/q-1<<endl;
       else
       cout<<m+sum/q<<endl;

   }




    return 0;
}