View Compilation Error

0_0_30383739_5608.cpp:13:1: error: 'set' does not name a type
 set<ll>s;
 ^
0_0_30383739_5608.cpp:14:1: error: 'set' does not name a type
 set<ll>::iterator it;
 ^
0_0_30383739_5608.cpp: In function 'int main()':
0_0_30383739_5608.cpp:25:3: error: 's' was not declared in this scope
   s.clear();
   ^
0_0_30383739_5608.cpp:36:5: error: 'it' was not declared in this scope
     it = s.lower_bound(a[i].x);
     ^
0_0_30383739_5608.cpp:46:8: error: 'it' was not declared in this scope
   for (it = s.begin(); it != s.end(); it++)
        ^