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#include<bits/stdc++.h>
#define VAR(i,n) __typeof(n) i = (n)
#define loop(i,j,s) for(int i=j;i<s;i++)
#define loopback(i,j,s) for(int i=j;i>=s;i--)
#define foreach(i,c) for(VAR(i,(c).begin());i!=(c).end();i++)
#define pln( x ) cout << x << "\n"
#define ps( x ) cout << x << " "
#define entr cout << "\n"
#define pcnt(i) __builtin_popcount(i)
#define ll long long
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define SIZE(c) (c).size()
#define ALL(c) (c).begin(), (c).end()
using namespace std;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef vector<vector<int> > VVI;
const int INFTY=20000000;
const int MAX=500100;
const int MOD=10000000;

void coutTab(int* tab,int n){
	loop(i,0,n){
		cout<<tab[i]<<" ";
	}
	cout<<"\n";
}

template<class T> void coutVec(vector<T> tab){
	for(T t : tab){
		cout<<t<<" ";
	}
	cout<<"\n";
}
//------------------------------------------
int a[MAX];
ll pref[MAX];
int dp[MAX];

ll get_pref(int i, int j){
	if(i==0) return pref[j];
	return pref[j]-pref[i-1];
}

int main(){
	ios_base::sync_with_stdio(0);
	int n;
	cin>>n;
	loop(i,0,n) cin>>a[i];
	pref[0]=a[0];
	loop(i,1,n) pref[i]=pref[i-1]+a[i];
	
	dp[0]= a[0] >= 0 ? 0 : -1;
	loop(i,0,n) {
		dp[i]=-1;
		if(a[i]==0) {
			dp[i]=dp[i-1];
			continue;
		}
		
		dp[i] = get_pref(0,i) >= 0 ? i : -1;
		loop(j,1,i+1) {
			if(get_pref(j,i)>=0&&dp[j-1]>=0) {
				dp[i]=min(i-j + dp[j-1], dp[i]);
			}
		}
	}
	//coutTab(dp, n);
	int mini = n+2;
	int j=n-1;
	while(j>=0 && a[j]>=0) {
		if(dp[j] != -1) mini=min(mini, dp[j]);
		j--;
	}
	if(j>=0 && dp[j]!=-1) mini=min(mini, dp[j]);
	
	if(mini==n+2) pln("-1");
	else pln(mini);
}