#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

ll n, m, mx, s, ans, t, sl, sr;
ll a[200100];
ll p[200100];
ll trl[800100];
ll trr[800100];
ll lz1[800100];
ll lz2[800100];
ll t1, t2;
ll que1[200100];
ll que2[200100];

inline bool ok1(ll x, ll y, ll z) {
	return (a[z] - a[x]) * (y - x) > (a[y] - a[x]) * (z - x);
}

inline bool ok2(ll x, ll y, ll z) {
	return (a[x] - a[z]) * (x - y) > (a[x] - a[y]) * (x - z);
}

void work() {
	t1 = 1;
	que1[t1] = sl;
	for (ll i = sl + 1; i < sr; i++) {
		while (t1 > 1 && ok1(que1[t1 - 1], que1[t1], i)) {
			t1--;
		}
		que1[++t1] = i;
	}
	que1[t1 + 1] = -1;
	t2 = 1;
	que2[t2] = sr;
	for (ll i = sr - 1; i > sl; i--) {
		while (t2 > 1 && ok2(que2[t2 - 1], que2[t2], i)) {
			t2--;
		}
		que2[++t2] = i;
	}
	que2[t2 + 1] = -1;
	return;
}

void build(ll l, ll r, ll idx) {
	lz1[idx] = lz2[idx] = 0; 
	if (l == r) {
		trl[idx] = 0;
		trr[idx] = m + 1;
	} else {
		ll mid = (l + r) >> 1;
		build(l, mid, idx << 1);
		build(mid + 1, r, idx << 1 | 1);
	}
	return;
}

inline void pd(ll idx) {
	if (lz1[idx]) {
		trl[idx << 1] = lz1[idx << 1] = lz1[idx];
		trl[idx << 1 | 1] = lz1[idx << 1 | 1] = lz1[idx];
		lz1[idx] = 0;
	}
	if (lz2[idx]) {
		trr[idx << 1] = lz2[idx << 1] = lz2[idx];
		trr[idx << 1 | 1] = lz2[idx << 1 | 1] = lz2[idx];
		lz2[idx] = 0;
	}
	return;
}

void upd1(ll l, ll r, ll idx, ll L, ll R, ll x) {
	if (L <= l && r <= R) {
		trl[idx] = x;
		lz1[idx] = x;
	} else {
		pd(idx);
		ll mid = (l + r) >> 1;
		if (L <= mid) {
			upd1(l, mid, idx << 1, L, R, x);
		}
		if (mid < R) {
			upd1(mid + 1, r, idx << 1 | 1, L, R, x);
		}
	}
	return;
}

void upd2(ll l, ll r, ll idx, ll L, ll R, ll x) {
	if (L <= l && r <= R) {
		trr[idx] = x;
		lz2[idx] = x;
	} else {
		pd(idx);
		ll mid = (l + r) >> 1;
		if (L <= mid) {
			upd2(l, mid, idx << 1, L, R, x);
		}
		if (mid < R) {
			upd2(mid + 1, r, idx << 1 | 1, L, R, x);
		}
	}
	return;
}

inline ll qry(ll l, ll r, ll idx, ll x) {
	if (l == r) {
		return trr[idx] - trl[idx];
	} else {
		pd(idx);
		ll mid = (l + r) >> 1;
		if (x <= mid) {
			return qry(l, mid, idx << 1, x);
		} else {
			return qry(mid + 1, r, idx << 1 | 1, x);
		}
	}
}

int main() {
	scanf("%lld%lld", &n, &m);
	a[0] = 0;
	a[n + 1] = m + 1;
	for (ll i = 1; i <= n; i++) {
		scanf("%lld", &a[i]);
	}
	sort(a + 1, a + n + 1);
	sl = 0;
	sr = n + 1;
	work();
	t1 = t2 = 2;
	while (sl < sr - 1) {
		if (que1[t1] > sr || que2[t2] < sl || que1[t1] == -1 || que2[t2] == -1) {
			work();
			t1 = t2 = 2;
			continue;
		}
		ll o1 = que1[t1];
		ll o2 = que2[t2];
		if ((a[o1] - a[sl]) * (sr - o2) <= (a[sr] - a[o2]) * (o1 - sl)) {
			if (o1 == sr) {
				o1--;
			}
			for (ll i = sl + 1; i <= o1; i++) {
				p[++t] = i;
			}
			sl = o1;
			t1++;
		} else {
			if (o2 == sl) {
				o2++;
			}
			for (ll i = sr - 1; i >= o2; i--) {
				p[++t] = i;
			}
			sr = o2;
			t2++;
		}
	}
	build(1, n, 1);
	for (ll i = 1; i <= n; i++) {
		ans += qry(1, n, 1, p[i]);
		upd2(1, n, 1, 1, p[i], a[p[i]]);
		upd1(1, n, 1, p[i], n, a[p[i]]);
	} 
	mx = max(mx, ans);
	printf("%lld\n", mx);
	return 0;
}