//  Created by conan1024hao in 2019.
//  Copyright © 2019 conan1024hao. All rights reserved.
//  専用ライブラリです、自由にコピーして構いません。
//  感谢看我的代码！Wechat:conan1024hao Twitter/QQ:810396815
#pragma GCC optimize ("O3")
#include <iostream>
#include <iomanip>
#include <istream>
#include <ostream>
#include <sstream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <queue>
#include <deque>
#include <list>
#include <stack>
#include <map>
#include <unordered_map>
#include <set>
#include <utility>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <ctime>
#include <cctype>
#include <cstdlib>
#define IINF 10e8
#define INF 10e16
#define MOD 1000000007
#define mod 1000000007
#define rep(i, a, n) for (ll i = a; i < (ll)(n); i++)
#define Endl endl
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define mmax(x,y)(x>y?x:y)
#define mmin(x,y)(x<y?x:y)
#define chmax(x,y) x=mmax(x,y)
#define chmin(x,y) x=mmin(x,y)
#define all(x) (x).begin(),(x).end()
#define siz(x) (ll)(x).size()
#define PI acos(-1.0)
using namespace std;
//using Int=int_fast64_t;
typedef long long int ll;
typedef pair<ll,ll>Pll;
typedef pair<int,int>Pin;
long long GCD(long long a, long long b) { return b ? GCD(b, a%b) : a; }
long long LCM(long long a, long long b)  {return a/GCD(a,b)*b;}
int dx[8]={-1,0,1,0,1,1,-1,-1};
int dy[8]={0,-1,0,1,1,-1,1,-1};
char dir[4]={'u','l','d','r'};
ll cmp1(pair<ll,string>a,pair<ll,string> b){
        if(a.fi!=b.fi)
        return a.fi<b.fi;
        else
        return a.se<b.se;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
int main(){//問題をちゃんと見ろ!!!!!!!!!!!!!!!!!      llか??????????        memset()!!!!!!!!!!!!       ペナを減らせ!!!!!!!!!!!!!
    cin.tie(0);
    ios::sync_with_stdio(false);
    //-------------------------------
    ll n;cin>>n;
    vector<ll>a(n);
    ll suma=0;
    for(ll i=0;i<n;i++){
        cin>>a[i];
        suma+=a[i];
    }
    vector<ll>b(n);ll ans=0;
    ll nokori=0;ll sumb=0;
    vector<ll>need;
    vector<ll>canuse;
    for(ll i=0;i<n;i++){
        cin>>b[i];sumb+=b[i];
        if(a[i]<b[i]){
            need.pb(b[i]-a[i]);
        }
        else if(a[i]>b[i])
            canuse.pb(a[i]-b[i]);
    }
    sort(all(canuse));reverse(all(canuse));
    if(sumb>suma){
        cout<<-1<<endl;
        return 0;
    }
    ll j=0;ll i;
   // ll now=-1;
    bool color[100001];
    memset(color,0,sizeof(color));
    for(i=0;i<canuse.size();i++){
        bool mm=0;
        //cout<<need[j]<<" "<<canuse[i]<<" "<<ans<<endl;
        if(j>=need.size())break;
        if(canuse[i]<need[j]){
            need[j]-=canuse[i];
            canuse[i]=0;
            color[i]=1;
        }
        else{
            canuse[i]-=need[j];
            need[j]=0;
            j++;
            mm=1;
            color[i]=1;
            ans++;
        }
        if(canuse[i]==0)ans++;
        if(mm==1)i--;
    }
    if(canuse[i]!=0&&color[i]==1)ans++;
    cout<<ans<<endl;
    //-------------------------------
    return 0;
}
//---------------------------------------------------------------------------









Measured memory_bytes: 2936