foo.cc: In function 'int main()':
foo.cc:20:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d",&N,&K);
     ~~~~~^~~~~~~~~~~~~~~
foo.cc:21:33: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for (int i=1;i<=K;i++) scanf("%d %d %d",&a[i],&b[i],&c[i]);
                            ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。