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// Jakub Rozek
// Elektrownie i fabryki [B]
// potyczki 2020
// O( n*log(n) )

#include <bits/stdc++.h>
using namespace std;

const int N=500005;
const int R=524288;

struct struc{
	long long w,sp;
	int p;
};

int n,q,qq,odp,r;
long long x;
vector <struc> v;
vector <long long> sp;
map <long long , int> m;
int dp[N];
int tree[R*2+2];

void insert(int a, int b)
{
	a+=r;
	while(a)
	{
		tree[a]=min(tree[a],b);
		a/=2;
	}
}

int query(int w, int a, int b, int c, int d)
{
	if(b<c || a>d) return 1000000009;
	if(c<=a && b<=d) return tree[w];
	else return min(query(w*2, a, (a+b)/2 ,c,d), query(w*2+1, (a+b)/2+1, b ,c,d));
	
}

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	v.push_back({0,0});
	sp.push_back(0);
	cin>>n;
	for(int i=1; i<=n; ++i)
	{
		cin>>x;
		if(x==0) continue;	
		
		if(v[q].sp<0)
		{
			sp.pop_back();
			odp+=i-qq;
			v[q].w+=x;
			v[q].sp+=x;
		}
		else
		{
			v.push_back({x, v[q].sp+x, i-odp});
			++q;
		}
		
		sp.push_back(v[q].sp);
		
		qq=i;
	}
	
	if(v[q].sp<0)
	{
		cout<<"-1";
		return 0;
	}
	
	sort(sp.begin(), sp.end());
	qq=0;
	x=-1000000009;
	for(int i=0; i<(int)sp.size(); ++i)
	{
		if(sp[i]==x) continue;
		x=sp[i];
		m[x]=qq;
		++qq;
	}
	
	r=1;
	while(r<=qq) r*=2;
	for(int i=1; i<2*r; ++i) tree[i]=1000000009;
	
	for(int i=1; i<=q; ++i)
	{
		insert(m[v[i-1].sp], dp[i-1]-v[i].p);
		
		dp[i]=v[i].p+query(1,0,r-1,0,m[v[i].sp]);
	}
	
	cout<<odp+dp[q];
	return(0);
}