foo.c: In function 'main':
foo.c:10:6: warning: implicit declaration of function 'ss' [-Wimplicit-function-declaration]
   if(ss(p)==1&&ss(a-p)==1)
      ^~
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&a);
  ^~~~~~~~~~~~~~

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