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#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#ifdef LOC
#include "debuglib.h"
#else
#define deb(...)
#define DBP(...)
#endif
using namespace std;
using   ll         = long long;
using   Vi         = vector<int>;
using   Pii        = pair<int, int>;
#define pb           push_back
#define mp           make_pair
#define x            first
#define y            second
#define rep(i, b, e) for (int i = (b); i < (e); i++)
#define each(a, x)   for (auto& a : (x))
#define all(x)       (x).begin(), (x).end()
#define sz(x)        int((x).size())

int main() {
	cin.sync_with_stdio(0); cin.tie(0);
	cout << fixed << setprecision(10);

	int n; cin >> n;
	vector<ll> pref = {0};

	rep(i, 0, n) {
		int k; cin >> k;
		pref.pb(pref.back() + k);
	}

	if (pref[0] > pref.back()) {
		cout << "-1\n";
		return 0;
	}

	vector<ll> dp(sz(pref)+5, INT64_MAX);

	rep(i, 1, sz(pref)-1) {
		if (pref[i] >= 0 && pref[i] <= pref.back()) {
			*upper_bound(all(dp), pref[i]) = pref[i];
		}
	}

	int ans = n-1 - int(lower_bound(all(dp), INT64_MAX) - dp.begin());
	cout << ans << '\n';
	return 0;
}