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#include <vector>
#include <iostream>
#include <sstream>
#include <math.h>
#include <sys/time.h>
#include <cstdlib>
#include <algorithm>
#include <cassert>
#include <cstring>
#include <fstream>
#include <set>
#include <map>
#include <iomanip>
#include <queue>

#define FOR(i,a,b)  for(__typeof(b) i=(a);i<(b);++i)
#define REP(i,a)    FOR(i,0,a)
#define FOREACH(x,c)   for(__typeof(c.begin()) x=c.begin();x != c.end(); x++)
#define ALL(c)      c.begin(),c.end()
#define CLEAR(c)    memset(c,0,sizeof(c))
#define SIZE(c) (int) ((c).size())

#define PB          push_back
#define MP          make_pair
#define X           first
#define Y           second

#define ULL         unsigned long long
#define LL          long long
#define LD          long double
#define II         pair<int, int>
#define DD         pair<double, double>
#define FF          pair<float,float>

#define VC	    vector
#define VI          VC<int>
#define VVI         VC<VI>
#define VVVI        VC<VVI>
#define VD          VC<double>
#define VS          VC<string>
#define VII         VC<II>
#define VDD         VC<DD>
#define VFF         VC<FF>
#define VVD         VC<VD>
#define VVVD        VC<VVD>
#define VULL         VC<ULL>

#define DB(a)       cerr << #a << ": " << a << endl;

using namespace std;

template<class T> void print(VC < T > v) {cerr << "[";if (SIZE(v) != 0) cerr << v[0]; FOR(i, 1, SIZE(v)) cerr << "," << v[i]; cerr << "]\n";}
template<class T> string i2s(T &x) { ostringstream o; o << x; return o.str(); }
VS split(string &s, char c = ' ') {VS all; int p = 0, np; while (np = s.find(c, p), np >= 0) {all.PB(s.substr(p, np - p)); p = np + 1;} if (p < SIZE(s)) all.PB(s.substr(p)); return all;}

#define INFTY 1000000
#define BLOCK 4000

int main(int argc, char *argv[]){
    int n;
    cin >> n;
    VC<LL> E(n+1,0);
    REP(i,n) cin >> E[i+1];

    VI C(n+1,INFTY);
    C[0] = 0;

    VC<pair<LL,int>> pto,pto2; // pairs (required energy,extra cost)
    pto.reserve(n+1);
    pto2.reserve(n+1);

    FOR(i,1,n+1){
        long long e = 0;
        int j = i;
        do{ 
            e += E[j];
            if (e >= 0)
                C[i] = min(C[i], C[j-1] + i-j);
            j--;
        } while (j > 0 && j%BLOCK != BLOCK-1);

        // get more solution using the previous block
        if (j != 0){
            //cout << "E" << e << endl;
            VC<pair<long long, int>>::iterator it = lower_bound(ALL(pto),MP(-e,0));
            if (it != pto.end())
                C[i] = min(C[i], i-j + it->Y);
        }
        //cout << C[i] << " ";

        // prepare next block
        if (i%BLOCK == BLOCK-1){
            pto2.clear();
            e = 0;
            for(int k=i; k>0; k--){
                e += E[k];
                pto2.PB(MP(e,i-k+C[k-1]));
            }
            sort(ALL(pto2));
            pto.clear();
            for(auto x : pto2){
                while (!pto.empty() && pto.back().Y > x.Y) pto.pop_back();
                pto.PB(x);
            }

            //cout << "[ ";
            //for(auto x : pto) cout << " (" << x.X << " , " << x.Y << ") ";
            //cout << " ]";
        }
    }

    if (C[n] < INFTY)
        cout << C[n] << endl;
    else
        cout << -1 << endl;

    return 0;  
}