aoj0551.cpp

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define PB push_back
#define INF (1LL<<61LL)

typedef pair<int, int> pii;

int N, L, a[100005], dx[] = {-1, 1};
vector<int> g[100005];
bool flg[100005];

int cal(int x) {
  int res = L - a[x], temp = 0;
  for (int i = 0; i < g[x].size(); ++i) {
    temp = max(temp, cal(g[x][i]));
  }

  return res + temp;
}

signed main() {
  fill(a, a + 100005, INF);
  cin >> N >> L;
  for (int i = 1; i <= N; ++i)
    cin >> a[i];

  for (int i = 1; i <= N; ++i) {
    int count = 0;
    for (int j = 0; j < 2; ++j) {
      if (a[i + dx[j]] < a[i]) {
	g[i].PB(i + dx[j]);
	count++;
      }
    }

    if ((count == 2) || (((i == 1) || (i == N)) && (count == 1)))
      flg[i] = true;
  }

  int maxt = 0;
  for (int i = 1; i <= N; ++i) {
    if (!flg[i]) continue;
    maxt = max(maxt, cal(i));
  }

  cout << maxt << endl;
  
  return 0;
}