foo.cc: In function 'void merge_sort(PII*, int, int, LL*, bool (*)(PII, PII))':
foo.cc:15:17: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   15 |     int mid = l + r >> 1;
      |               ~~^~~
foo.cc: In function 'int main()':
foo.cc:48:5: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
   48 |     for (int i = 1; i <= n; i++)
      |     ^~~
foo.cc:51:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   51 |         printf("%d\n", ans);
      |         ^~~~~~

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