#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define sz(s)    (int)(s.size())
#define endl "\n"
#define PI acos(-1)
#define all(a) a.begin(), a.end()

void Open() {
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);
#endif  !ONLINEJUDGE
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
}
int dx[]{ 1, -1, 0, 0, 1, 1, -1, -1 };
int dy[]{ 0, 0, 1, -1, 1, -1, 1, -1 };
const int OO = 0x3f3f3f3f;
int dp[300005];
int n;
ll v[300005], b[300005];
int solve(int x)
{
	if (x == n + 1)
		return 0;
	int& ret = dp[x];
	if (~ret)return ret;
	ret = 1e9;
	if (b[x] >= v[x]) {
		ret = solve(x + 1) + 1;
	}
	else
	{
		ll cnt = 0;
		for (int i = x; i <= n; i++)
		{
			cnt++;
			if (b[i] >= v[i])
			{
				if (i != n) {
					
					ret = min((ll)ret, solve(i + 1) + (cnt*3) -2);
				}
				else {
					ret = min((ll)ret, solve(i + 1) + (cnt) +(cnt -1));
				}
			}
		}
	}
	return ret;


}

int main()
{
	//Open();
	cin >> n;
	memset(dp, -1, sizeof dp);
	for (int i = 1; i <= n; i++)cin >> v[i], v[i] += v[i - 1];
	for (int i = 1; i <= n; i++)cin >> b[i], b[i] += b[i - 1];
	
	b[0] = -1;
	v[0] = 0;
	if (v[n] > b[n])cout<<("-1");
	else cout << (ll)solve(1)-1+v[n];

}