WA x3，应该有些细节没有注意到

#include<iostream>
#include<algorithm>
using namespace std;
#define int long long
struct node{
	int id,num;
}a[200005];
bool cmp(node x,node y){
	return x.id<y.id;
}

signed main(){
	int n,m;
	cin>>n>>m;
	for(int i=1;i<=m;i++) cin>>a[i].id;
	for(int i=1;i<=m;i++) cin>>a[i].num;
	sort(a+1,a+m+1,cmp);
	int p=n,cnt=m,ans=0;
	while(cnt>=1){
		if(p-a[cnt].id+1<a[cnt].num){
			cout<<-1;
			return 0;
		}
		p-=a[cnt].num;
		ans+=(p+1-a[cnt].id+p+a[cnt].num-a[cnt].id)*a[cnt].num/2;
		cnt--;
	}
	cout<<ans;
	return 0;
}