View Compilation Error

0_0_33549636_6862.cpp:27:1: error: 'unordered_map' does not name a type
 unordered_map<unsigned long long,int> M;
 ^
0_0_33549636_6862.cpp: In function 'void init()':
0_0_33549636_6862.cpp:31:2: error: 'M' was not declared in this scope
  M[1]=1,M[2]=2;
  ^
0_0_33549636_6862.cpp: In function 'int main()':
0_0_33549636_6862.cpp:53:10: error: 'M' was not declared in this scope
    cout<<M[res]<<'\n';
          ^