foo.cc:3:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main() 
      ^
foo.cc: In function 'int main()':
foo.cc:12:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=1;i<=n;i+=2){
          ~^~~

自豪的采用jd5进行评测(github.com/masnn/jd5)

{"receive":"2020-02-28T12:36:55.787Z","handle":"2020-02-28T12:36:55.787Z","cache_start":"2020-02-28T12:36:55.787Z","read_cases":"2020-02-28T12:36:56.498Z","judge":"2020-02-28T12:36:56.500Z","done":"2020-02-28T12:36:57.017Z"}