rt，不明白为什么答案错误

#include<bits/stdc++.h>
using namespace std;
int a[500005];
signed main(){
	int n,k;
	cin >> n >> k;
	n *= 2;
	for(int i = 1;i <= n;++i){
		cin >> a[i];
	}
	for(int i = 1;i <= n;++i){
		if(i % 2 == 1){
			int sum = 0,xx = i % k;
			for(int j = 1;j <= n;++j){
				if(j % k == xx){sum += a[j];}
			}
			a[i] = sum % i;
		}
	}
	for(int i = 1;i <= n;++i){
		cout << a[i] << " ";
	}
}