Main.c:1:1: error: unknown type name 'def'
    1 | def chengjie(n):
      | ^~~
Main.c: In function 'chengjie':
Main.c:1:16: error: expected declaration specifiers before ':' token
    1 | def chengjie(n):
      |                ^
Main.c:1:5: warning: type of 'n' defaults to 'int' [-Wimplicit-int]
    1 | def chengjie(n):
      |     ^~~~~~~~
Main.c:15: warning: control reaches end of non-void function [-Wreturn-type]