foo.c: In function 'SetUnion':
foo.c:6:17: warning: unused variable 'flag' [-Wunused-variable]
    6 | { int d[20]={0},flag=0,k=0;
      |                 ^~~~
foo.c: In function 'main':
foo.c:21:7: warning: unused variable 'i' [-Wunused-variable]
   21 | { int i,n1,n2,n3;
      |       ^
foo.c: In function 'input':
foo.c:4:18: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    4 |  for(i=0;i<n;i++)scanf("%d",&a[i]);}
      |                  ^~~~~~~~~~~~~~~~~
foo.c: In function 'main':
foo.c:23:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   23 |  scanf("%d %d %d",&n1 ,&n2 ,&n3);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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