import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        int n  = fs.nextInt();
        int[] a = new int[n];
        int[] b = new int[n];
        long sumA,sumB;
        sumA = sumB = 0;
        for (int i = 0; i < n; i++) {
            a[i] = fs.nextInt();
            sumA+=a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = fs.nextInt();
            sumB += b[i];
        }
        if(sumA < sumB){
            System.out.println(-1);
            return;
        }
        int res = 0;
        long remain = 0;
        int[] diff = new int[n];
        for (int i = 0; i < n; i++) {
            if(a[i] < b[i]){
                remain += b[i] - a[i];
                res++;
            }else{
                diff[i] = a[i]-b[i];
            }
        }
        Arrays.sort(diff);
        for(int i=n-1;i>=0 && remain > 0;i--) {
            remain -= diff[i];
            res++;
        }
        System.out.println(res);

    }

    static class FastScanner {
        private final InputStream in = System.in;
        private final byte[] buffer = new byte[1024];
        private int ptr = 0;
        private int buflen = 0;

        private boolean hasNextByte() {
            if (ptr < buflen) {
                return true;
            } else {
                ptr = 0;
                try {
                    buflen = in.read(buffer);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (buflen <= 0) {
                    return false;
                }
            }
            return true;
        }

        private int readByte() {
            if (hasNextByte()) return buffer[ptr++];
            else return -1;
        }

        private static boolean isPrintableChar(int c) {
            return 33 <= c && c <= 126;
        }

        public boolean hasNext() {
            while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
            return hasNextByte();
        }

        public String next() {
            if (!hasNext()) throw new NoSuchElementException();
            StringBuilder sb = new StringBuilder();
            int b = readByte();
            while (isPrintableChar(b)) {
                sb.appendCodePoint(b);
                b = readByte();
            }
            return sb.toString();
        }

        public long nextLong() {
            if (!hasNext()) throw new NoSuchElementException();
            long n = 0;
            boolean minus = false;
            int b = readByte();
            if (b == '-') {
                minus = true;
                b = readByte();
            }
            if (b < '0' || '9' < b) {
                throw new NumberFormatException();
            }
            while (true) {
                if ('0' <= b && b <= '9') {
                    n *= 10;
                    n += b - '0';
                } else if (b == -1 || !isPrintableChar(b)) {
                    return minus ? -n : n;
                } else {
                    throw new NumberFormatException();
                }
                b = readByte();
            }
        }

        public int nextInt() {
            long nl = nextLong();
            if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
            return (int) nl;
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }
    }
}

Measured memory_bytes: 37636