RE了最后一个 不知道问题在哪里 求教

#include<bits/stdc++.h>
using namespace std;
int n,a[1000005],q[10000005],l,r,ans;
int main(){
    cin >> n;
    for(int i = 1;i <= n; i++){
        cin >> a[i];
        a[i+n] = a[i];
    }
    for(int i = 1;i <= n*2; i++){
        while(l <= r&&i-q[l] > n/2)
			l ++;
        if(l <= r)
			ans = max(ans,a[i]+a[q[l]]+i-q[l]);
        while(l <= r&&a[q[r]]-q[r] <= a[i]-i)
			r--;
        q[++r]=i;
    }
    cout<<ans;
}