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#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <unordered_map>
using namespace std;

typedef long long int LL;
typedef long double LD;
typedef vector<int> VI;
typedef vector<LL> VLL;
typedef vector<LD> VLD;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;

const int INF = 1000000001;
const LD EPS = 10e-9;

#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 FORE(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define MP make_pair
#define PB push_back
#define ST first
#define ND second
#define abs(a) ((a)<0 ? -(a) : (a))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))

int n, a;
LL sum;
bool wasNegative;
vector<pair<int, int>> nonZeros;

vector<pair<int, int>> numToSegments(int num, const int len)
{
    vector<pair<int, int>> res;

    int idx = 0;
    while(idx <= len)
    {
        if((num&1) == 0)
        {
            if(res.empty() || res.rbegin()->second != idx)
            {
                res.push_back(make_pair(idx, idx));
            }

            ++idx;
            num >>= 1;
        }
        else
        {
            const int oldIdx = idx;
            while((num&1) > 0 && idx < len)
            {
                ++idx;
                num >>= 1;
            }

            res.push_back(make_pair(oldIdx, idx));
        }
    }

    return res;
}

int solveFor(const vector<pair<int, int>>& numSegments)
{
    int len = 0;
    for(const auto& elem : numSegments)
    {
        LL sumInSeg = 0;

        for(int i = elem.first; i <= elem.second; ++i)
        {
            sumInSeg += nonZeros[i].first;

            if(i > elem.first)
            {
                len += (nonZeros[i].second - nonZeros[i-1].second);
            }
        }

        if(sumInSeg < 0)
        {
            return -1;
        }
    }


    return len;
}

int main()
{
    cin >> n;

    for(int i = 0; i < n; ++i)
    {
        cin >> a;
        sum += a;

        if(a != 0)
        {
            nonZeros.push_back(make_pair(a, i));
        }

        if(a < 0)
        {
            wasNegative = true;
        }
    }

    if(sum < 0)
    {
        cout << "-1" << endl;
        return 0;
    }

    if(!wasNegative)
    {
        cout << "0" << endl;
        return 0;
    }

    int segmentsCount = nonZeros.size()-1;
    int setUpperBound = (1 << segmentsCount);
    int minLen = INF;

    for(int i = 1; i < setUpperBound; ++i)
    {
        const auto numSegments = numToSegments(i, segmentsCount);
        const int segLen = solveFor(numSegments);

        if(segLen > -1)
        {
            if(segLen < minLen)
            {
                minLen = segLen;
            }
        }
    }

    cout << minLen << endl;

    return 0;
}