foo.c: In function 'Merge':
foo.c:16:6: warning: unused variable 'N' [-Wunused-variable]
   16 |  int N;
      |      ^
foo.c:15:6: warning: unused variable 'j' [-Wunused-variable]
   15 |  int j;
      |      ^
foo.c: In function 'main':
foo.c:32:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   32 |  scanf("%d %d %d", &n1, &n2, &n3);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.c:38:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   38 |   scanf("%d", &a1[i]);
      |   ^~~~~~~~~~~~~~~~~~~
foo.c:44:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   44 |   scanf("%d", &a2[i]);
      |   ^~~~~~~~~~~~~~~~~~~
foo.c:47:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   47 |   scanf("%d", &a3[i]);
      |   ^~~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务