func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     long long n, m;     cin >> n >> m;     long long on[n + 2];     long long is[n + 1];     int inst[n + 2];     is[0] = 1;     int pval = m;     inst[0] = 0;     for (int i(1); i <= n; i++) {       cin >> inst[i];       if (is[i - 1] == 0) {         is[i] = 1;       } else         is[i] = 0;     }     inst[n + 1] = m;     if (is[n] == 1) {       on[n] = m - inst[n];       pval = inst[n];     } else {       on[n] = 0;       pval = inst[n];     }     for (int i(n - 1); i >= 1; --i) {       if (is[i] == 1) {         on[i] = on[i + 1] + (pval - inst[i]);         pval = inst[i];       } else {         on[i] = on[i + 1];         pval = inst[i];       }     }     on[0] = on[1] + inst[1] - 0;     pval = 0;     on[n + 1] = 0;     long long ans = on[0];     for (int i(0); i <= n; i++) {       if (inst[i + 1] - inst[i] < 2) {         continue;       } else {         long long l, m1, r;         l = on[0] - on[i];         m1 = inst[i + 1] - inst[i] - 1;         r = m - inst[i + 1] - on[i + 1];         ans = max(ans, l + m1 + r);       }     }     cout << ans;   }   