foo.c: In function 'F':
foo.c:15:1: warning: control reaches end of non-void function [-Wreturn-type]
   15 | }
      | ^
foo.c: In function 'main':
foo.c:20:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   20 |  scanf("%d%d",&b1,&a1);
      |  ^~~~~~~~~~~~~~~~~~~~~
foo.c:21:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   21 |  scanf("%d%d",&b2,&a2);
      |  ^~~~~~~~~~~~~~~~~~~~~

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