foo.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:6:2: error: 'cin' undeclared (first use in this function)
    6 |  cin>>n;
      |  ^~~
foo.c:6:2: note: each undeclared identifier is reported only once for each function it appears in
foo.c: At top level:
foo.c:8:1: error: expected identifier or '(' before 'return'
    8 | return 0;
      | ^~~~~~

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