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

typedef long long LL;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;

#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()

template<typename _T> inline void _DBG(const char *s, _T x) { cerr << s << " = " << x << "\n"; }
template<typename _T, typename... args> void _DBG(const char *s, _T x, args... a) { while(*s != ',') cerr << *s++; cerr << " = " << x << ','; _DBG(s + 1, a...); }

#ifdef LOCAL
#define _upgrade ios_base::sync_with_stdio(0);
#define DBG(...) _DBG(#__VA_ARGS__, __VA_ARGS__)
#else
#define _upgrade ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define DBG(...) (__VA_ARGS__)
#define cerr if(0) cout
#endif

// ********************** CODE ********************** //

const int N = 5e5 + 7;
const int MAX = 1 << 19;
const LL INF = 1e18;

LL tree[2 * MAX];

void update(int e, LL v)
{
    tree[e + MAX] = v;
    for(int i = (e + MAX) / 2; i >= 1; i /= 2)
        tree[i] = min(tree[2 * i], tree[2 * i + 1]);
}

LL query(int a, int b)
{
    a += MAX, b += MAX;
    LL ans = min(tree[a], tree[b]);
    while(a / 2 != b / 2)
    {
        if(a % 2 == 0) ans = min(ans, tree[a + 1]);
        if(b % 2 == 1) ans = min(ans, tree[b - 1]);
        a /= 2, b /= 2;
    }
    return ans;
}

int n;
LL a[N], p[N];
pair<LL, int> events[N];

int main()
{
    _upgrade
    
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        cin >> a[i];
        p[i] = p[i - 1] + a[i];
        events[i] = {p[i], i};
    }

    if(p[n] < 0)
    {
        cout << -1 << "\n";
        return 0;
    }

    for(int i = 0; i <= n; i++)
        tree[i + MAX] = INF;
    for(int i = MAX - 1; i >= 1; i--)
        tree[i] = min(tree[2 * i], tree[2 * i + 1]);


    sort(events, events + n + 1);

    for(int id = 0; id <= n; id++)
    {
        int i = events[id].second;
        if(i == 0)
            update(0, -1);
        else
        {
            LL dp = min(INF, query(0, i - 1) - 1);
            update(i, dp);
        }
    }

    cout << query(n, n) + n + 1 << "\n";

    return 0;
}