View Compilation Error

0_0_39416090_1578.cpp:11:1: error: 'set' does not name a type
   11 | set<pii> st;
      | ^~~
0_0_39416090_1578.cpp: In function 'int main()':
0_0_39416090_1578.cpp:15:17: error: 'st' was not declared in this scope; did you mean 'std'?
   15 |                 st.clear();
      |                 ^~
      |                 std
0_0_39416090_1578.cpp:21:27: error: 'sf' was not declared in this scope
   21 |                         ++sf;
      |                           ^~