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#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using D = double;
#define f1 first
#define f2 second
#define randint(a, b) uniform_int_distribution<int>{a, b}(gen)
#ifdef LOC
void OUT() {cout << '\n';}
template<class H, class ... T> void OUT(H h, T ... t)
{
	cout << h << ' ';
	OUT(t...);
}
#define P(...) cout << "[" << #__VA_ARGS__ << "] ", OUT(__VA_ARGS__)
#else
#define P(...)
#define OUT(...)
#endif
//mt19937 gen;

int n;
LL val[500100];

struct TR
{
	int id;
	LL val;
	bool operator<(const TR & a) const
	{
		return val < a.val;
	}
};

TR tree[1<<20];
LL dp[500100];

int elToTree[500100];

vector<pair<int, int>> prefs;
int depth = 4;

void updateSingle(int i)
{
	if(tree[2 * i] < tree[2 * i + 1]) tree[i] = tree[2 * i];
	else tree[i] = tree[2 * i + 1];
}

void update(int p)
{
	while(p > 1)
	{
		p /= 2;
		updateSingle(p);
	}
}

void setTree(int p)
{
	tree[elToTree[p] + depth].val = dp[p] - p;
	update(elToTree[p] + depth);
}

TR getMin(int st, int en, int a = 0, int b = depth - 1, int p = 1)
{
	if(st <= a && b <= en) return tree[p];
	if(b < st || en < a) return {-1, 999999999};
	return min(getMin(st, en, a, (a+b) / 2, p * 2), getMin(st, en, (a+b) / 2 + 1, b, p * 2 + 1));
}

void pr()
{
	for(int i = 1; i < 2 * depth; ++i)
	{ cout << tree[i].id << ' ' << tree[i].val << " | ";}
	cout << '\n';
}

int main(int, char ** /*args*/)
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	//gen.seed(atoi(args[1]));
	cin >> n;
	++n;
	LL prefsum = 0;
	val[0] = 0;
	prefs.push_back({0, 0});
	for(int i = 1; i < n; ++i)
	{
		cin >> val[i];
		prefsum += val[i];
		prefs.push_back({prefsum, i});
	}
	sort(prefs.begin(), prefs.end());
	while(n + 3 >= depth) depth *= 2;
	for(int i = 0; i < (int) prefs.size(); ++i)
	{
		elToTree[prefs[i].f2] = i;
	}
	for(int i = 0; i < depth; ++i)
		tree[depth + i] = {i, 999999999};
	for(int i = depth - 1; i >= 0; --i)
		updateSingle(i);
	dp[0] = 0;
	setTree(0);
	for(int i = 1; i < n; ++i)
	{
		auto t = getMin(0, elToTree[i] - 1);
		//pr();
		//P(t.val, elToTree[i]);
		if(t.val > 10000000)
			dp[i] = 10000100 + i - 1;
		dp[i] = t.val + i - 1;
		if(val[i] >= 0)
		{
			dp[i] = min(dp[i], dp[i - 1]);
		}
		//P(dp[i]);
		setTree(i);
	}
	if(dp[n - 1] < 10000000)
		cout << dp[n - 1] << '\n';
	else cout << -1 << '\n';
	/*for(int i = 0; i < n; ++i)
	{
		cout << dp[i] << ' ';
	}*/
	return 0;
}