text: #include <iostream>
  using namespace std;
  
  int main()
  {
      int size;
      cin >> size;
      int array[size];
      for (int i = 0; i < size; i++) {
          cin >> array[i];
      }
      int sum = ((size + 1) * (size + 2)) / 2;
  
      int total = 0;
      for (int i = 0; i < n; i++) {
          total = total + array[i];
      }
      cout << "\nThe missing number\t:\t" << (sum - total);
  }
  