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#include <iostream>
#include <deque>
#include <algorithm>
#include <set>
#include <vector>

using namespace std;

int main() {
    int n;
    cin >> n;
    std::deque<long long> diffs;
    for (int i = 0; i < n; ++i) {
        long long val;
        cin >> val;
        diffs.push_back(val);
    }

    long long sum_positive = 0;
    long long sum_negative = 0;
    

    for (int i = 0; i < n; ++i) {
        if (diffs[i] > 0) sum_positive += diffs[i];
        else sum_negative += diffs[i];
    }

    long long balance = sum_positive + sum_negative;
    if (balance < 0) {
        cout << -1;
        return 0;
    }

    int road = 0;
    bool change = true;

    while (change) {
        change = false;
        while (!diffs.empty() && diffs.back() <= 0) {
            long long el = diffs.back();
            diffs.pop_back();
            if (el < 0) ++road;
            if (!diffs.empty()) diffs.back() += el;
            change = true;
        }
        
        while(diffs.size() > 1 && diffs.back() > 0 && diffs[diffs.size() - 1] >= -diffs[diffs.size() - 2]) {
            long long el = diffs.back();
            diffs.pop_back();
            ++road;
            diffs.back() += el;
            change = true;
        }

        while (!diffs.empty() && diffs.front() <= 0) {
            long long el = diffs.front();
            diffs.pop_front();
            if (el < 0) ++road;
            if (!diffs.empty()) diffs.front() += el;
            change = true;
        }

        while(diffs.size() > 1 && diffs[0] > 0 && diffs[0] >= -diffs[1]) {
            long long el = diffs.front();
            diffs.pop_front();
            ++road;
            diffs.front() += el;
            change = true;
        }

    }

    if (balance == 0 || diffs.size() == 0 ) {
        cout << road + diffs.size();
        return 0;
    }


}