foo.c: In function 'main':
foo.c:11:2: warning: implicit declaration of function 'memset' [-Wimplicit-function-declaration]
   11 |  memset(q,0,4*n);
      |  ^~~~~~
foo.c:11:2: warning: incompatible implicit declaration of built-in function 'memset'
foo.c:3:1: note: include '<string.h>' or provide a declaration of 'memset'
    2 | #include <stdlib.h>
  +++ |+#include <string.h>
    3 | int main()
foo.c:8:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    8 |  scanf("%d",&n);
      |  ^~~~~~~~~~~~~~
foo.c:14:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   14 |  scanf("%d %d",&a,&b);
      |  ^~~~~~~~~~~~~~~~~~~~

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