line.cpp: In function 'void append(int, int)':
line.cpp:11:23: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
11 | if (o >= 2 && (o & o - 1) == 0)
| ~~^~~
line.cpp: In function 'int main()':
line.cpp:20:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
20 | scanf("%d%d", &n, &m);
| ~~~~~^~~~~~~~~~~~~~~~
line.cpp:24:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
24 | scanf("%d%d", &i, &j), i--, j--;
| ~~~~~^~~~~~~~~~~~~~~~