/in/foo.cc: In function 'int main()':
/in/foo.cc:33:7: warning: unused variable 'lena' [-Wunused-variable]
   33 |   int lena=a.size();
      |       ^~~~
/in/foo.cc:37:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   37 |   scanf("%d",&per);
      |   ~~~~~^~~~~~~~~~~
/in/foo.cc:38:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   38 |   scanf("%d",&n);
      |   ~~~~~^~~~~~~~~
/in/foo.cc:40:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   40 |    scanf("%d %d",&x,&y);
      |    ~~~~~^~~~~~~~~~~~~~~