/in/foo.c:1:1: error: unknown type name 'def'
 def f(n):
 ^~~
/in/foo.c: In function 'f':
/in/foo.c:1:9: error: expected declaration specifiers before ':' token
 def f(n):
         ^
/in/foo.c:1:5: warning: type of 'n' defaults to 'int' [-Wimplicit-int]
 def f(n):
     ^
/in/foo.c:8:1: warning: control reaches end of non-void function [-Wreturn-type]
 print(f(n))
 ^~~~~