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#include <bits/stdc++.h>
using namespace std;
#define mk make_pair
#define fst first
#define sz(x) x.size()
#define snd second
#define pb push_back
#define VAR(v) #v << " = " << v << " "
#define debug if(0)
#define M_PI 3.14159265358979323846
typedef complex<long double> C;
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ll> Matrix;
const int maxn = (int)11e5 + 9;
const int INF = (int)1e9 + 7;
int mod = (int)1e9 + 7;
ll tab[maxn], pref[maxn];
int T[maxn];
int n, N = 1;

void add(int pos, int val){
    pos += N;
    T[pos] = val; pos /= 2;
    while(pos){
        T[pos] = min(T[2*pos], T[2*pos+1]);
        pos /= 2;
    }
}

int query(int l, int r){
    l += N, r += N;
    int ret = INF;
    while(l < r)
    {
        //debug cout << VAR(l) << VAR(r) << endl;
        if(l&1)
            ret = min(ret, T[l++]);
        if(!(r&1))
            ret = min(ret, T[r--]);
        l /= 2, r /= 2;
    }
    if(l == r)
        ret = min(ret, T[l]);
    return ret;
}

ll toBin[maxn];
int PosInTree[maxn];
void Prep(){
    while(N <= n) N *= 2;
    for(int i = 0; i <= 2*N; i++)
        T[i] = INF;
    vector<pair<ll, int>> vec;
    for(int i = 0; i <= n; i++)
        vec.pb(mk(pref[i], i));
    sort(vec.begin(), vec.end());
    for(int i = 0; i < vec.size(); i++){
        pair<ll, int> p = vec[i];
        PosInTree[p.snd] = i;
        toBin[i] = p.fst;
    }
    debug{
        cout<<VAR(n) << VAR(N) << endl;
        for(int i = 0; i <= n + 1; i++){
            cout<<VAR(i)<<endl;
            cout << VAR(pref[i]) << VAR(tab[i]) << VAR(PosInTree[i])<<endl;
        }
        for(int i = 0; i <= n; i++)
            cout<<i<<"\t";
        cout<<endl;
        for(int i = 0; i <= n; i++)
            cout<<toBin[i]<<"\t";
        cout<<endl;
    }
}

int get_range(ll x){
    int low = 0, high = n + 2;
    while(high - low > 1){
        int mid = (low + high)/2;
        //debug cout << VAR(mid) << VAR(x) << VAR(toBin[mid])<<endl;
        if(x >= toBin[mid])
            low = mid;
        else
            high = mid;
    }
    return low;
}

void ComputeDp(){
    add(PosInTree[0], -1);
    for(int k = 1; k <= n; k++){
        int range = get_range(pref[k]);
        ll val = query(0, range);
        debug cout << VAR(k) << VAR(pref[k]) << VAR(PosInTree[k]) << VAR(range) << VAR(val) <<endl;
        add(PosInTree[k], val - 1);
        debug{
            for(int i = 0; i <= n; i++)
                cout<<i<<"\t";
            cout<<endl;
            for(int i = 0; i <= n; i++)
                cout<<query(i, i)<<"\t";
            cout<<endl;
        }
    }
}

int main(int argc, char* argv[])
{
    ios::sync_with_stdio(false);
    debug; else cin.tie(NULL), cout.tie(NULL);
    cin>>n;
    for(int i = 1; i <= n; i++){
        cin>>tab[i];
        pref[i] = pref[i-1] + tab[i];
    }
    debug cout << "OK"<<endl;
    Prep();
    ComputeDp();
    int res = query(PosInTree[n], PosInTree[n]) + n + 1;
    if(res <= n)
        cout<<res<<"\n";
    else
        cout<<-1<<"\n";
    debug{
        for(int i = 0; i <= n; i++)
            cout<<query(PosInTree[i], PosInTree[i]) + i + 1<<" ";
        cout<<endl;
    }
    return 0;
}