foo.cc: In function 'int top2(int)':
foo.cc:44:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.cc: In function 'int main()':
foo.cc:47:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&n,&m);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:48:34: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(int i=1; i<=n; ++i) scanf("%d",&a[i]);
                             ~~~~~^~~~~~~~~~~~
foo.cc:51:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&x,&y);
         ~~~~~^~~~~~~~~~~~~~

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