foo.c: In function 'main':
foo.c:21:9: warning: 'fgets' writing 10001 bytes into a region of size 10000 overflows the destination [-Wstringop-overflow=]
   21 |         fgets(s2,10001,stdin);
      |         ^~~~~~~~~~~~~~~~~~~~~
foo.c:19:14: note: destination object 's2' of size 10000
   19 |         char s2[10000];
      |              ^~
In file included from foo.c:1:
/nix/store/y8wfrgk7br5rfz4221lfb9v8w3n0cnyd-glibc-2.37-8-dev/include/stdio.h:592:14: note: in a call to function 'fgets' declared with attribute 'access (write_only, 1, 2)'
  592 | extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
      |              ^~~~~

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