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#include <bits/stdc++.h>
#include <unistd.h>
#include <sstream>
using namespace std;
#define REP(i,n) for(int _n=(n), i=0;i<_n;++i)
#define FOR(i,a,b) for(int i=(a),_b=(b);i<=_b;++i)
#define FORD(i,a,b) for(int i=(a),_b=(b);i>=_b;--i)
#define TRACE(x) cerr << "TRACE(" #x ")" << endl;
#define DEBUG(x) cerr << #x << " = " << (x) << endl;
typedef long long LL; typedef unsigned long long ULL;


#define BIGMOD 1000012177LL
#define INF 1000000000

struct Building
{
    LL mx;
    int pos;

    // pozycje na glownej liscie
    //int sameTypeLeft, sameTypeRight;
    //int otherTypeLeft, otherTypeRight;

    // na wewnetrznych listach: elektrownie i fabryki
    //int idxOnList;
    //int otherListIdx;

    int bestScore;


    Building(LL v, int p) 
    : mx(v)
    , pos(p)
    , bestScore(0)
    //, sameTypeLeft(-1)
    //, sameTypeRight(-1)
    //, otherTypeLeft(-1)
    //, otherTypeRight(-1)
    //, idxOnList(0)
    //, otherListIdx(0)
    {}

    /*string toString() {
        ostringstream oss;
        char t = mx < 0 ? 'C' : 'P';
        //oss << t << "(p=" << pos << ",mx=" << mx << ")";
        //oss << t << "(p=" << pos << "," << used << "/" << mx << ",[" << sameTypeLeft << "," << sameTypeRight << "],[" << otherTypeLeft << "," << otherTypeRight << "])";
        return oss.str();
    }*/
};


void selftest()
{
    //solveSlow({2,-5,0,2,0,0,0,4,0,0,-1,4,0,0,0,0,-3});
    //solveSlow({5,5,0,0,0,-10,0,0,0,-1,10,1});
}

/*
void calculateNeighbours(vector<Building> &buildings, const vector<Building> &elektrownie, const vector<Building> &fabryki)
{
    int eIdx = 0;
    for (int i=0; i < buildings.size(); i++)
    {
        Building &b = buildings[i];

        if (b.mx > 0)
        {
            int prev = b.idxOnList - 1;
            int next = b.idxOnList + 1;
            b.sameTypeLeft = (prev >= 0) ? elektrownie[prev].pos : -1;
            b.sameTypeRight = (next < elektrownie.size()) ? elektrownie[next].pos : -1;
        }

        if (b.mx < 0)
        {
            int prev = b.idxOnList - 1;
            int next = b.idxOnList + 1;
            b.sameTypeLeft = (prev >= 0) ? fabryki[prev].pos : -1;
            b.sameTypeRight = (next < fabryki.size()) ? fabryki[next].pos : -1;
        }
    }
    for (int i=0; i < buildings.size(); i++)
    {
        Building &b = buildings[i];
        if (b.mx > 0)
        {
            int prev = b.otherListIdx - 1;
            int next = prev + 1;
            b.otherTypeLeft =  (prev >= 0) ? fabryki[prev].pos : -1;
            b.otherTypeRight = (next < fabryki.size()) ? fabryki[next].pos : -1;
        }
        
        if (b.mx < 0)
        {
            int prev = b.otherListIdx - 1;
            int next = prev + 1;
            b.otherTypeLeft =  (prev >= 0) ? elektrownie[prev].pos : -1;
            b.otherTypeRight = (next < elektrownie.size()) ? elektrownie[next].pos : -1;
        }
    }
}
*/

LL solve(vector<Building> &buildings)
{
    if (buildings.size() < 1)
    {
        return 0;
    }
    vector<LL> prefixSum(buildings.size() + 1);
    prefixSum[0] = 0;
    for (int i=1; i <= buildings.size(); i++)
    {
        prefixSum[i] = prefixSum[i-1] + buildings[i-1].mx;
        //printf("%lld ", prefixSum[i]);
    }
    if (prefixSum[buildings.size()] < 0)
    {
        return -1;
    }
    //printf("\n");
    
    for (int i=0; i < buildings.size(); i++)
    {
        Building &b = buildings[i];
        //printf("\n%s \n", b.toString().c_str());
        if (prefixSum[i+1] < 0)
        {
            b.bestScore = INF;
            //printf("prefixSum %lld below zero, skipping\n", prefixSum[i+1]);
            continue;
        }

        int withCurrentBest = INF;
        for (int k=i; k >= 0; --k)
        {
            Building &middle = buildings[k];
            int dist = b.pos - middle.pos;
            if (dist > withCurrentBest)
            {
                break;
            }
            if (prefixSum[i+1] - prefixSum[k] >= 0)
            {
                //printf("prefixSum allows better result at k=%d\n", k);
                int rightHalf = dist;
                
                int leftHalf = 0;
                if (k-1 >= 0)
                {
                    leftHalf = buildings[k-1].bestScore;
                }
                //printf("leftHalf=%d,rightHalf=%d\n", leftHalf, rightHalf);
                withCurrentBest = min(withCurrentBest, leftHalf + rightHalf);
                //printf("found better K at pos %d\n", middle.pos);
            }
        }
        b.bestScore = withCurrentBest;
        //printf("bestScore=%d\n", b.bestScore);
    }
    return buildings[buildings.size() -1 ].bestScore;
}

int main() {
    int n;
    selftest();
    scanf("%d", &n);
    vector<Building> elektrownie;
    vector<Building> fabryki;
    vector<Building> buildings;
    for (int i=0; i < n; i++)
    {
        LL x;
        scanf("%lld", &x);
        Building b(x,i);
        if (x > 0)
        {
            //b.idxOnList = elektrownie.size();
            //b.otherListIdx = fabryki.size();
            elektrownie.emplace_back(b);
        }
        if (x < 0)
        {
            //b.idxOnList = fabryki.size();
            //b.otherListIdx = elektrownie.size();
            fabryki.emplace_back(b);
        }
        if (x) buildings.emplace_back(b);
    }
    //calculateNeighbours(buildings, elektrownie, fabryki);
    //printf("total buildings: %d\n", buildings.size());
    LL answer = solve(buildings);
    printf("%lld\n", answer);
    return 0;
}