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#include <bits/stdc++.h>
using namespace std;
#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 {
#ifdef LOCAL
~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 << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
// debug & operator << (debug & dd, P p) { dd << "(" << p.x << ", " << p.y << ")"; return dd; }



int main() {
	int n;
	scanf("%d", &n);
	vector<long long> pref(n + 1);
	for(int i = 1; i <= n; ++i) {
		int a;
		scanf("%d", &a);
		pref[i] = pref[i-1] + a;
	}
	
	// coordinate compression
	vector<long long> values = pref;
	sort(values.begin(), values.end());
	values.resize( unique(values.begin(), values.end()) - values.begin());
	auto get_id = [&](long long x) {
		return lower_bound(values.begin(), values.end(), x) - values.begin();
	};
	
	int base = 1;
	while(base <= n) {
		base *= 2;
	}
	const int INF = 1e9 + 5;
	vector<int> tree(2 * base, INF);
	auto update = [&](int i, int value) {
		for(int pos = base + i; pos >= 1; pos /= 2) {
			tree[pos] = min(tree[pos], value);
		}
	};
	update(get_id(pref[0]), 0);
	int answer = INF;
	int prev_best = 0;
	for(int i = 1; i <= n; ++i) {
		if(pref[i] < pref[i-1]) {
			answer = INF;
		}
		int my_id = get_id(pref[i]);
		int R = base + my_id;
		int best = tree[R];
		while(R > 1) {
			if(R % 2 == 1) {
				best = min(best, tree[R-1]);
			}
			R /= 2;
		}
		best += i - 1;
		if(pref[i] >= pref[i-1]) {
			best = min(best, prev_best);
		}
		debug() << imie(i) imie(best);
		answer = min(answer, best);
		update(my_id, best - i);
		prev_best = best;
	}
	if(answer > INF / 2) {
		answer = -1;
	}
	printf("%d\n", answer);
}