foo.cc: In function 'int main()':
foo.cc:19:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   19 |         scanf("%lld%lld",&a,&b);
      |         ~~~~~^~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务