/in/foo.cc: In function 'int main()':
/in/foo.cc:7:26: warning: 'N' is used uninitialized [-Wuninitialized]
    7 |         vector<int> arr(2*N+1);
      |                         ~^~
/in/foo.cc:6:13: note: 'N' was declared here
    6 |         int N;
      |             ^