#include <iostream>
#include <vector>

using namespace std;

int min_r;

struct city{
    int value;
    int distance=0;
};


int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    
    int n;
    cin >> n;
    
    min_r = n;
    
    vector<struct city>cities;

    bool ft = false;
    
    struct city new_city;

    for(int i=0; i<n; i++){
        int num;
        cin >> num;
        
        if(num != 0){
            ft = true;
            new_city.value = num;
            cities.push_back(new_city);
            new_city.distance = 1;
        }else if(ft && num == 0){
            new_city.distance++;
        } 
    }
    
    cities[0].distance = 0;
    
    new_city.value = 0;
    new_city.distance = 0;
    
    cities.push_back(new_city);

    for(long long i=0; i<(1<<(cities.size()-2)); i++){
        vector<bool> roads;
        for(long long j=0; j<cities.size()-2; j++){
            if(((i>>j)&1)==1){
                roads.push_back(false);
            }else{
                roads.push_back(true);
            }
        }
        
        
        long long cur_value = cities[0].value;
        int cur_r = 0;
        
        for(int i=0; i<roads.size(); i++){
            if(roads[i] == false){
                if(cur_value<0){
                    break;
                }else{
                    cur_value = cities[i+1].value;
                }
            }else{
                cur_r += cities[i+1].distance;
                cur_value += cities[i+1].value;
            }
        }
        
        if(cur_value>=0){
            min_r = min(min_r, cur_r);
        }
        
    }
    
    if(min_r == n){
        cout << -1;
    }else{
        cout << min_r;
    }
}