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#include <bits/stdc++.h>

using namespace std;

typedef vector<int> VI;
typedef long long LL;
#define FOR(x, b, e) for(int x = b; x<= (e); ++x)
#define FORD(x, b, e) for(int x = b; x>= (e); --x)
#define REP(x, n) for(int x = 0; x<(n); ++x)
#define VAR(v, n)typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB pushback
#define ST first
#define ND second

int first_greater(LL *arr, int size, LL number) {
    LL *it = upper_bound(arr, arr+size, number);
    return it - arr;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int n;
    cin >> n;

    int a[n + 1];
    LL S[n + 1];
    S[0] = 0;
    FOR(i, 1, n) {
        cin >> a[i];
        S[i] = S[i - 1] + a[i];
    }

    if (S[0] > S[n]) {
        cout << "-1\n";
    }
    else {
        int length;
        LL A[n + 10];
        int wsk = 1;
        while ((S[wsk] < 0 || S[wsk] > S[n]) && wsk < n) {
            wsk++;
        }
        if (wsk == n) {
            length = 0;
        }
        else {
            FOR(i, 1, n + 9) {
                A[i] = 10000000000000000;
            }
            A[0] = S[wsk];
            FOR(i, wsk + 1, n - 1) {
                if (S[i] >= 0 && S[i] <= S[n]) {
                    A[first_greater(A, n + 10, S[i])] = S[i];
                }
            }

            length = 0;
            while (A[length] != 10000000000000000) {
                length++;
            }
        }

        cout << n - 1 - length << "\n";
    }

    return 0;
}