#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef vector<long long> vll;
typedef pair<int,int> pint;
typedef pair<long long, long long> pll;

#define MP make_pair
#define PB push_back
#define ALL(s) (s).begin(),(s).end()
#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P) 
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P) 
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P) 
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s; }





template<class T> struct Edge {
    int from, to;
    T cost;
    Edge(int f, int t, T c) : from(f), to(t), cost(c) {}
    friend bool operator < (const Edge &e1, const Edge &e2) {return e1.cost < e2.cost;}
    friend bool operator > (const Edge &e1, const Edge &e2) {return e1.cost > e2.cost;}
    friend ostream& operator << (ostream& s, const Edge<T>& E) {
        return s << E.from << "->" << E.to << '(' << E.cost << ')';
    }
};

const int MAX_V = 100100;
template<class T> struct Graph {
    int V;
    vector<Edge<T> > list[MAX_V];
    
    Graph(int n = 0) : V(n) {}
    void init(int n = 0) {V = n; for (int i = 0; i < MAX_V; ++i) list[i].clear();}
    inline vector<Edge<T> >& operator [] (int i) {return list[i];}
    
    void direct(int f, int t, T c) {
        list[f].push_back(Edge<T>(f,t,c));
    }
    
    friend ostream& operator << (ostream& s, const Graph& G) {
        s << endl; for (int i = 0; i < G.V; ++i) {s << i << " : " << G.list[i] << endl;}return s;
    }
};

Graph<long long> G;

int N, L, w;
int s, t;
long long REM[MAX_V];
long long dp[MAX_V];


long long rec(int v) {
    if (v == t) return dp[v] = 0;
    
    long long res = -1;
    for (int i = 0; i < G[v].size(); ++i) {
        rec(G[v][i].to);
    }
    
    for (int i = 0; i < G[v].size(); ++i)
        chmax(res, dp[G[v][i].to] + G[v][i].cost);
    
    //cout << v << " : " << res << endl;
    
    return dp[v] = res;
}

int main() {
    while (cin >> N >> L) {
        for (int i = 0; i < MAX_V; ++i) REM[i] = L+1;
        for (int i = 0; i < N; ++i) cin >> w, REM[i+1] = L - w;
        
        G.init(N+2);
        s = 0, t = N+1;
        
        for (int i = 1; i <= N; ++i) {
            if (REM[i] < REM[i-1] && REM[i] < REM[i+1]) {
                G.direct(s, i, 0);
            }
            G.direct(i, t, REM[i]);
        }
        for (int i = 1; i < N; ++i) {
            if (REM[i] < REM[i+1]) G.direct(i, i+1, REM[i]);
            else G.direct(i+1, i, REM[i+1]);
        }
        
        //COUT(G);
        
        memset(dp, -1, sizeof(dp));
        long long res = rec(s);
        
        cout << res << endl;
    }
    return 0;
}


Measured memory_bytes: 11552