foo.cc: In function 'bool cp(xs, xs)':
foo.cc:10:33: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  return a.yw>b.yw || a.yw==b.yw && a.sx>b.sx;
                      ~~~~~~~~~~~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:13:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("students.in","r",stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:14:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("students.out","w",stdout);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

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