foo.cc:3:1: error: expected identifier before 'int'
    3 | int main()
      | ^~~
foo.cc:2:16: error: expected ';' before 'int'
    2 | using namespace
      |                ^
      |                ;
    3 | int main()
      | ~~~             
foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope
    6 |  cin<<n1<<n2
      |  ^~~

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