foo.cc: In function 'int main()':
foo.cc:21:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(ri i=1;i<=n;i++)
  ^~~
foo.cc:26:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   cout<<ans<<endl;
   ^~~~
foo.cc:16:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&n);
  ~~~~~^~~~~~~~~
foo.cc:26:9: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
   cout<<ans<<endl;
         ^~~

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