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#include <vector>
#include <cstdio>
#include <map>
#include <algorithm>
#include <climits>

int main() {

    int n;
    scanf("%d", &n);

    std::vector<long> a(n, 0);
    for (int i = 0; i < n; ++i)
        scanf("%ld", &a[i]);

    // moc -> koszt poczatkowy + poczatek
    std::map<long long, std::pair<unsigned long long,int>> costs;

    costs[0] = std::make_pair(0, 0);
    long long power_offset = 0;
    int last_i = 0;

    for (int i = 0; i < n; ++i) {
        if (a[i] != 0) {
            if (costs.rbegin()->first + power_offset >= 0) {
                
                auto c = costs.upper_bound(-power_offset-1);
                if ((c->first + power_offset) >= 0) {
                    unsigned long long min_cost = c->second.first + (last_i - c->second.second);

                    auto it = costs.find(-power_offset);
                    if (it == costs.end() || ((it->second.first + (i - it->second.second)) >= min_cost)) {
                        costs[-power_offset] = std::make_pair(min_cost, i);

                        it = costs.find(-power_offset);
                        if (std::next(it) != costs.end())
                            it++;

                        min_cost = it->second.first + (i - it->second.second);
                        while (it != costs.begin()) {
                            --it;
                            if (min_cost < it->second.first + (i - it->second.second)) {
                                //printf("erase %lld %lld\n", it->first + power_offset, min_cost);
                                it = costs.erase(it);
                            }
                            min_cost = std::min(min_cost, it->second.first + (i - it->second.second));
                        }
                    }
                }
            }

            power_offset += a[i];
            last_i = i;

            /*
            printf("i: %d, = %ld, ps = %lld\n", i, a[i], power_offset);
            for (const auto &c : costs) {
                printf("\t%lld -> %lld (cost: %lld, i: %d)\n", c.first + power_offset, c.second.first + (last_i - c.second.second), c.second.first, c.second.second);
            }//*/
        }
    }

    auto c = costs.upper_bound(-power_offset-1);
    if (c->first + power_offset >= 0) {
        printf("%lld\n", c->second.first + (last_i - c->second.second));
    } else {
        puts("-1");
    }

    return 0;
}