/in/foo.c: In function 'main':
/in/foo.c:14:7: warning: implicit declaration of function 'scanf_s' [-Wimplicit-function-declaration]
  Koop:scanf_s("%d%d", &L, &M);
       ^~~~~~~
/in/foo.c:26:3: warning: statement with no effect [-Wunused-value]
   for (start; start < end + 1; start++)
   ^~~
/tmp/cc3ZFRku.o: In function `main':
foo.c:(.text.startup+0x54): undefined reference to `scanf_s'
foo.c:(.text.startup+0x94): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status