#include <bits/stdc++.h>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class T> inline T sqr(T x) {return x*x;}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define exist(s,e) ((s).find(e)!=(s).end())
#define range(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)  range(i,0,n)
#define clr(a,b) memset((a), (b) ,sizeof(a))
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi  = acos(-1.0);
const ll INF =1LL << 62;
const int inf =1 << 29;

int n;

ll p[100010];
ll l[100010];

ll sum[100010];

ll merge_count(vector<ll> &a){
	int n=a.size();
	if(n<=1)
		return 0;
	ll cnt=0;
	vector<ll> b(a.begin(),a.begin()+n/2);
	vector<ll> c(a.begin()+n/2,a.end());

	cnt+=merge_count(b);
	cnt+=merge_count(c);

	int ai=0,bi=0,ci=0;
	while(ai<n){
		if(bi<b.size()&&(ci==c.size()||b[bi]<=c[ci])){
			a[ai++]=b[bi++];
		}else{
			cnt+=n/2-bi;
			a[ai++]=c[ci++];
		}
	}
	return cnt;
}


int main(void){
	cin >> n;
	rep(i,n) cin >> p[i];
	rep(i,n) cin >> l[i];

	vector<ll> res;

	rep(i,n){
		if(i-1>=0) sum[i]+=sum[i-1];
		sum[i]+=p[i];
		res.pb(sum[i]);
	}

	ll ans=merge_count(res);

	bool ok=true;
	rep(i,n){
		ll cur=res[i];
		if(i-1>=0) cur-=res[i-1];
		if(cur<l[i]) ok=false;
	}
	if(ok)
		cout << ans << endl;
	else
		cout << -1 << endl;
	return 0;
}