/in/foo.cc: In function 'void merge_sort(PII*, int, int, LL*, bool (*)(PII, PII))':
/in/foo.cc:26:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
     int mid = l + r >> 1;
               ~~^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:61:5: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     for (int i = 1; i <= n; i++)
     ^~~
/in/foo.cc:64:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  printf("%d\n", ans);
  ^~~~~~