foo.cc:3:7: error: expected nested-name-specifier before 'namespaces'
 using namespaces std;
       ^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:7:33: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(int i=1;i<=13;i++) scanf("%d",&a[i]);
                            ~~~~~^~~~~~~~~~~~

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