Language: C++

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

//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx,avx2,fma")

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;
typedef pair<int, ll> pil;
typedef vector<pii> vpii;
typedef vector<pil> vpil;
typedef vector<pli> vpli;
typedef set<int> si;
typedef set<ll> sll;
typedef map<int, int> mii;
typedef map<int, ll> mil;
typedef map<ll, int> mli;
typedef map<ll, ll> mll;

const double pi = acos(-1.0);
const long long INF = 2e18;

#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define sz size()
#define in insert
#define endl "\n"
#define sqr(a)((a) *(a))
#define jor(a) !(a & 1)	// jor means EVEN number
#define bjor(a)(a & 1)	// bjor means ODD number
#define all(a) a.begin(), a.end()
#define mem(arr, b) memset(arr, b, sizeof(arr))	//memset only for -1 and 0
//fill(a, a+n, 5)	//fill for any value
#define for0(i, b) for (int i = 0; i < (b); i++)
#define for1(i, b) for (int i = 1; i <= (b); i++)
#define forab(i, a, b) for (int i = (a); i <= (b); i++)
#define forba(i, b, a) for (int i = (b); i >= (a); i--)
#define rep(i, a, b, c) for (int i = (a); i != (b); i += (c))
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

#define fileRead freopen("input.txt", "r", stdin);

void print(int a[], int n)
{
	// for testing or debugging
	for (int i = 0; i < n; i++) cout << a[i] << " ";
	cout << endl;
}

//______________________________________________________\\

main()
{
    IOS;
    //fileRead;
    int x,y;
    cin>>x>>y;
    si s; 
    int n;
    while(y--) cin>>n, s.in(n);
    int l=x, r=x;
    while(1){
        if(s.count(l)==0) {cout<<l; break;}
        if(s.count(r)==0) {cout<<r; break;}
        l--,r++;
    }
}

Compiler output:
a.cc:1:2: error: stray '#' in program
    1 | c#include <bits/stdc++.h>
      |  ^
a.cc:1:1: error: 'c' does not name a type
    1 | c#include <bits/stdc++.h>
      | ^
a.cc:10:9: error: 'vector' does not name a type
   10 | typedef vector<int> vi;
      |         ^~~~~~
a.cc:11:9: error: 'vector' does not name a type
   11 | typedef vector<ll> vll;
      |         ^~~~~~
a.cc:12:9: error: 'pair' does not name a type
   12 | typedef pair<int, int> pii;
      |         ^~~~
a.cc:13:9: error: 'pair' does not name a type
   13 | typedef pair<ll, int> pli;
      |         ^~~~
a.cc:14:9: error: 'pair' does not name a type
   14 | typedef pair<int, ll> pil;
      |         ^~~~
a.cc:15:9: error: 'vector' does not name a type
   15 | typedef vector<pii> vpii;
      |         ^~~~~~
a.cc:16:9: error: 'vector' does not name a type
   16 | typedef vector<pil> vpil;
      |         ^~~~~~
a.cc:17:9: error: 'vector' does not name a type
   17 | typedef vector<pli> vpli;
      |         ^~~~~~
a.cc:18:9: error: 'set' does not name a type
   18 | typedef set<int> si;
      |         ^~~
a.cc:19:9: error: 'set' does not name a type
   19 | typedef set<ll> sll;
      |         ^~~
a.cc:20:9: error: 'map' does not name a type; did you mean 'mp'?
   20 | typedef map<int, int> mii;
      |         ^~~
      |         mp
a.cc:21:9: error: 'map' does not name a type; did you mean 'mp'?
   21 | typedef map<int, ll> mil;
      |         ^~~
      |         mp
a.cc:22:9: error: 'map' does not name a type; did you mean 'mp'?
   22 | typedef map<ll, int> mli;
      |         ^~~
      |         mp
a.cc:23:9: error: 'map' does not name a type; did you mean 'mp'?
   23 | typedef map<ll, ll> mll;
      |         ^~~
      |         mp
a.cc:25:19: error: 'acos' was not declared in this scope
   25 | const double pi = acos(-1.0);
      |                   ^~~~
a.cc: In function 'void print(int*, int)':
a.cc:53:37: error: 'cout' was not declared in this scope
   53 |         for (int i = 0; i < n; i++) cout << a[i] << " ";
      |                                     ^~~~
a.cc:54:9: error: 'cout' was not declared in this scope
   54 |         cout << endl;
      |         ^~~~
a.cc: At global scope:
a.cc:59:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   59 | main()
      | ^~~~
a.cc: In function 'int main()':
a.cc:46:13: error: 'ios' has not been declared
   46 | #define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
      |             ^~~
a.cc:61:5: note: in expansion of macro 'IOS'
   61 |     IOS;
      |     ^~~
a.cc:46:38: error: 'cin' was not declared in this scope; did you mean 'in'?
   46 | #define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
      |                                      ^~~
a.cc:61:5: note: in expansion of macro 'IOS'
   61 |     IOS;
      |     ^~~
a.cc:46:50: error: 'cout' was not declared in this scope
   46 | #define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
      |                                                  ^~~~
a.cc:61:5: note: in expansion of macro 'IOS'
   61 |     IOS;
      |     ^~~
a.cc:65:5: error: 'si' was not declared in this scope; did you mean 'pi'?
   65 |     si s;
      |     ^~
      |     pi
a.cc:67:24: error: 's' was not declared in this scope
   67 |     while(y--) cin>>n, s.in(n);
      |                        ^
a.cc:70:12: error: 's' was not declared in this scope
   70 |         if(s.count(l)==0) {cout<<l; break;}
      |            ^
a.cc:71:12: error: 's' was not declared in this scope
   71 |         if(s.count(r)==0) {cout<<r; break;}
      |            ^