func_code_string: #include <bits/stdc++.h>   using namespace std;   using ll = long long;   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     ;     ll n, m;     cin >> n >> m;     std::vector<int> a(n + 2);     n = n + 2;     a[0] = 0;     a[n - 1] = m;     for (int i = 1; i <= n; i++) cin >> a[i];     ll v[n][2];     v[n - 1][0] = 0;     v[n - 1][1] = 0;     for (int i = n - 2; i >= 0; i--) {       v[i][0] = v[i + 1][1];       v[i][1] = (a[i + 1] - a[i]) + v[i + 1][0];     }     ll ans = v[0][1];     ll cur = 0;     for (int i = 0; i < n - 1; i++) {       int f;       if (i % 2 == 0)         f = 1;       else         f = 0;       if (f == 1) {         if (a[i + 1] - a[i] > 1) {           ans = max(ans, cur + a[i + 1] - 1 - a[i] + v[i + 1][1]);         }         cur += a[i + 1] - a[i];       } else {         if (a[i + 1] - a[i] > 1) {           ans = max(ans, cur + a[i + 1] - (a[i] + 1) + v[i + 1][0]);         }       }     }     cout << ans;     return 0;   }   