foo.c: In function 'main':
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ^~~~~~~~~~~~~~~
foo.c: In function 'f':
foo.c:32:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.c: In function 'judge':
foo.c:51:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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