WA3个点，难受

#include <bits/stdc++.h>
#define el "\n"
#define sp " "
#define fi first
#define se second
#define inf 1e18
#define r0 return 0
#define int long long
#define F(i, a, b, c) for (int i = a; i <= b; i += c)
#define debug printf ("Yuexingfei_qwq\n")
#define TheEnd continue
#define base(s) s = sp + s

using namespace std;

typedef long long ll;
typedef string str;
using ull = unsigned ll;

int n, m;
int ans = 0, s = 0;
struct Info {
	int x, a;
} a[210000];

inline bool cmp(Info x, Info y) {
	return x.x < y.x;
}

signed main(void) {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);
	std::cout.tie(0);
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		cin >> a[i].x;
	}
	for (int i = 1; i <= m; i++) {
		cin >> a[i].a;
		s += a[i].a;
	}
	sort(a + 1, a + m + 1, cmp);
	for (int i = 1; i < m; i++) {
		if (a[i].a > a[i + 1].x - a[i].x) {
			int p = a[i].a - (a[i + 1].x - a[i].x);
			a[i + 1].a += a[i].a - (a[i + 1].x - a[i].x);
			a[i].a = a[i + 1].x - a[i].x;
			ans += (a[i + 1].x - a[i].x) * p;
		}
	}
	for (int i = 1; i < m; i++) {
		if (a[i + 1].x - a[i].x > a[i].a) {
			cout << -1 << el;
			r0;
		}
	}
	if (n - a[m].x > a[m].a) {
		cout << -1 << el;
		r0;
	}
	if (s != n) {
		cout << -1 << el;
		r0;
	}
	for (int i = 1; i < m; i++) {
		int y = a[i + 1].x - a[i].x - 1;
		ans += (y + 1) * y / 2;
	}
	int y = n - a[m].x;
	if (y > 0) {
		ans += (y + 1) * y / 2;
	}
	cout << ans << el;
	r0;
}