コンパイルエラー

./Main.cpp:3:2: error: invalid preprocessing directive #[
    3 | #[fastout]
      |  ^
./Main.cpp:1:1: error: 'use' does not name a type
    1 | use proconio::{fastout, input};
      | ^~~
./Main.cpp:4:1: error: 'fn' does not name a type
    4 | fn main() {
      | ^~