macro_rules! debug {
    ( $x:ident [ $i:expr ] ) => {
        if cfg!(debug_assertions) {
            println!("{}[{}] = {}", stringify!($x), $i, $x[$i]);
        }
    };
    ( $x:ident [ $i:expr ][ $j:expr ] ) => {
        if cfg!(debug_assertions) {
            println!("{}[{}][{}] = {}", stringify!($x), $i, $j, $x[$i][$j]);
        }
    };
    ( $x:expr ) => {
        if cfg!(debug_assertions) {
            println!("{}:{} {} = {:?}", line!(), column!(), stringify!($x), $x);
        }
    };
}

fn main() {
    let stdin = std::io::stdin();
    let mut stdin = my::io::InputReader::new(stdin.lock());

    let N: usize = stdin.read();
    let mut A = vec![0i64; N];
    let mut B = vec![0i64; N];
    for i in 0..N {
        A[i] = stdin.read();
    }
    for i in 0..N {
        B[i] = stdin.read();
    }
    let A_sum: i64 = A.iter().sum();
    let B_sum: i64 = B.iter().sum();
    if A_sum >= B_sum {
        let mut result = 0;
        let mut overs = Vec::new();
        let mut under = 0;
        for i in 0..N {
            if A[i] < B[i] {
                under += B[i] - A[i];
                result += 1;
            } else if A[i] > B[i] {
                overs.push(A[i] - B[i]);
            }
        }
        overs.sort();
        for x in overs.iter().rev() {
            if under <= 0 {
                break;
            }
            under -= *x;
            result += 1;
        }
        println!("{}", result);
    } else {
        println!("-1");
    }
}

mod my {
    pub mod io {
        use std::io::{BufRead, ErrorKind, Result};
        use std::str::{FromStr, from_utf8};
        use std::fmt::Debug;

        pub fn read_word<R: BufRead>(r: &mut R, buf: &mut Vec<u8>)
                                              -> Result<usize> {
            let mut read = 0;
            loop {
                let (done, used) = {
                    let available = match r.fill_buf() {
                        Ok(n) => n,
                        Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
                        Err(e) => return Err(e)
                    };
                    match available.iter().position(|&x| x == b'\n' || x == b' ') {
                        Some(i) => {
                            buf.extend_from_slice(&available[..i]);
                            (true, i + 1)
                        }
                        None => {
                            buf.extend_from_slice(available);
                            (false, available.len())
                        }
                    }
                };
                r.consume(used);
                read += used;
                if done || used == 0 {
                    return Ok(read);
                }
            }
        }

        pub struct InputReader<R: BufRead> {
            reader: R,
            buf: Vec<u8>,
        }

        impl<R: BufRead> InputReader<R> {
            pub fn new(reader: R) -> InputReader<R> {
                InputReader {
                    reader: reader,
                    buf: Vec::<u8>::new(),
                }
            }

            pub fn read_word(&mut self) {
                read_word(&mut self.reader, &mut self.buf);
            }
            
            pub fn read<T>(&mut self) -> T
                where T: FromStr,
                      T::Err: Debug
            {
                self.buf.clear();
                self.read_word();
                from_utf8(&self.buf).unwrap().trim().parse().unwrap()
            }
        }
    }
}

Measured memory_bytes: 6396