/in/foo.cc: In function 'int main()':
/in/foo.cc:9:18: error: 'scanf_s' was not declared in this scope
  scanf_s("%d", &n);
                  ^
/in/foo.cc:23:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for (int i = 0; i < n-1; i++)
  ^~~
/in/foo.cc:31:3: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
   set<int>::iterator it = nums.end();
   ^~~