/in/foo.cc: In function 'int main()':
/in/foo.cc:14:19: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
 #define fo(i,a,b) for(R int (i)=(a);(i)<=(b);++(i))
                   ^
/in/foo.cc:42:2: note: in expansion of macro 'fo'
  fo(i,1,n*2)if(sum[i])ans+=sum[i]*(sum[i]-1)/2;printf("%lld\n",ans);
  ^~
/in/foo.cc:42:48: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  fo(i,1,n*2)if(sum[i])ans+=sum[i]*(sum[i]-1)/2;printf("%lld\n",ans);
                                                ^~~~~~