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#include <bits/stdc++.h>
using namespace std;
//{
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define VAR(v, i) __typeof(i) v=(i)
#define all(v) (v).begin(),(v).end()
#define FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)


#define PII pair<int,int>
#define st first
#define nd second
#define pb push_back
#define lint long long int
#define VI vector<int>

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
	*this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
};
//{
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

#define make( x) int (x); scanf("%d",&(x));
#define make2( x, y) int (x), (y); scanf("%d%d",&(x),&(y));
#define make3(x, y, z) int (x), (y), (z); scanf("%d%d%d",&(x),&(y),&(z));
#define make4(x, y, z, t) int (x), (y), (z), (t); scanf("%d%d%d%d",&(x),&(y),&(z),&(t));
#define makev(v,n) VI (v); FOR(i,0,(n)) { make(a); (v).pb(a);} 
#define IOS ios_base::sync_with_stdio(0)
#define HEAP priority_queue

#define read( x) scanf("%d",&(x));
#define read2( x, y) scanf("%d%d",&(x),&(y));
#define read3(x, y, z) scanf("%d%d%d",&(x),&(y),&(z));
#define read4(x, y, z, t) scanf("%d%d%d%d",&(x),&(y),&(z),&(t));
#define readv(v,n) FOR(i,0,(n)) { make(a); (v).pb(a);}
#define jeb() fflush(stdout);
//}

const int max_n = 500005;
const int INF = 1e9;
int dp[max_n];

int n;
int in[max_n];
int nr_suf[max_n];

vector<pair<lint, int> > suf;
int sufixow = 0;

int szykuj_sufixy() {
	sort(all(suf));
	lint act = suf[0].st;
	int nr = 0;
	FOR(i,0,n+1) {
		if (suf[i].st == act) {
			nr_suf[suf[i].nd] = nr;
		} else {
			nr++;
			act = suf[i].st;
			nr_suf[suf[i].nd] = nr; 
		}
	}
	return nr + 1;
}

int N;
VI rt;

void init_rt(){
	for(N=1; N<sufixow; N<<=1);
	rt = VI(N<<1);
	FOR(i,0,N) rt[i+N] = INF;
	FORD(i,N-1,1){
		rt[i] = min(rt[i<<1],rt[(i<<1)|1]);
	}
}

// w przedziale x,y reprezentowanym przez v
// szukaj przedziału l,r
int rob(int v, int x, int y, int l, int r){
	if(l > r) return INF;
	if( l == x &&  r == y){
		return rt[v];
	}
	int mid = (x+y)/2;
	int a1 = rob(2*v,x,mid,l,min(r,mid));
	int a2 = rob(2*v+1,mid+1,y,max(l,mid+1),r);
	return min(a1, a2);
}

void change_rt(int v, int x){
	if (x >= rt[v+N]) return;

	rt[v+N] = x;
	for(int j = (v+N)>>1; j ; j>>=1){
		rt[j] = min(rt[j<<1],rt[(j<<1)|1]);
	}
}

int get_min(int x) {
	return rob(1, 0, N-1, 0, x);
}



int main() {
	read(n);
	lint sum = 0;
	FOR(i,0,n) {
		make(a); in[i] = a;
	}
	suf.pb({sum,n});
	FORD(i,n-1,0) {
		sum += in[i];
		suf.pb({sum,i});
	}
	if (sum < 0) {
		printf("-1\n");
		return 0;
	}
	sufixow = szykuj_sufixy();
	init_rt();
	dp[n] = 0;
	change_rt(nr_suf[n], dp[n] + n);
	FORD(i,n-1,0) {
		dp[i] = get_min(nr_suf[i]) - i - 1;
		change_rt(nr_suf[i], dp[i] + i);
	}

	printf("%d\n", dp[0]);
}