answer.code: In function ‘int main()’:
answer.code:9:9: error: ‘unordered_map’ was not declared in this scope
    9 |         unordered_map<int,int> M ;
      |         ^~~~~~~~~~~~~
answer.code:9:9: note: ‘std::unordered_map’ is only available from C++11 onwards
answer.code:9:23: error: expected primary-expression before ‘int’
    9 |         unordered_map<int,int> M ;
      |                       ^~~
answer.code:14:17: error: ‘M’ was not declared in this scope
   14 |             if(!M[t+1]){
      |                 ^
answer.code:17:13: error: ‘M’ was not declared in this scope
   17 |             M[t]=1;
      |             ^