foo.cc: In function 'int main()':
foo.cc:19:2: warning: statement has no effect [-Wunused-value]
   19 |  0;
      |  ^
foo.cc: At global scope:
foo.cc:21:5: error: redefinition of 'int main()'
   21 | int main()
      |     ^~~~
foo.cc:3:5: note: 'int main()' previously defined here
    3 | int main()
      |     ^~~~

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