View Compilation Error

0_0_30063742_15669.cpp: In function 'int main()':
0_0_30063742_15669.cpp:34:11: error: 'cin' was not declared in this scope
     while(cin>>n>>k)
           ^
0_0_30063742_15669.cpp:49:9: error: 'cout' was not declared in this scope
         cout<<sum<<endl;
         ^
0_0_30063742_15669.cpp:49:20: error: 'endl' was not declared in this scope
         cout<<sum<<endl;
                    ^