int n, k, s = 0;
cin >> n >> k;
for (int i = 0; i < n; ++i) {
    int x;
    cin >> x;
    s += x;
}
for (int ans = 0;; ans++) {
    int a = 2 * (s + ans * k);
    int b = (2 * k - 1) * (ans + n);

    if (a >= b) {
    	cout << ans;
    	return 0;
    }
}

for (int i = 0; i < n; i++) {
	cin >> k[i] >> l[i];
	a.push_back(make_pair(min(2 * k[i], l[i]) - min(k[i], l[i]), i));
}
sort(a.rbegin(), a.rend());

long long ans = 0;
for (int i = 0; i < f; i++) {
	int pos = a[i].second;
	ans += min(2 * k[pos], l[pos]);
}
for (int i = f; i < n; i++) {
	int pos = a[i].second;
	ans += min(k[pos], l[pos]);
}
cout << ans;