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#include <bits/stdc++.h>
using namespace std;

#define debug if(0)
#define err stderr
#define pb push_back
#define mp make_pair
#define ff first
#define ss second

#define MAXN 500005
#define ZAK 1048580

typedef long long int ll;

int n;
ll tab[MAXN], dp[MAXN], mini, maxi, q, R;
ll INF = (ll)(1e18) + 5;

struct Node;
typedef struct Node* Tree;
Tree tree = NULL;

struct Node {
    ll value;
    Tree left, right;    
};

void insert(Tree* tree, ll pp, ll pk, ll gdzie, ll war) {
    if (*tree == NULL) {
        Tree nowy = (Node*) malloc(sizeof(struct Node));
        nowy->left = nowy->right = NULL;
        nowy->value = INF;
        
        *tree = nowy;
    }
    
    (*tree)->value = min((*tree)->value, war);
    
    if (pp == pk) {
        return;
    }
    
    ll sr = (pp + pk) / 2;
    
    if (gdzie <= sr) {
        insert(&(*tree)->left, pp, sr, gdzie, war);
    } else {
        insert(&(*tree)->right, sr + 1, pk, gdzie, war);
    }
}

ll query(Tree* tree, ll pp, ll pk, ll zp, ll zk) {
    if (*tree == NULL) {
        return INF;
    }
    
    if (pk < zp || zk < pp) {
        return INF;
    }
    
    if (zp <= pp && pk <= zk) {
        return (*tree)->value;
    }
    
    ll sr = (pp + pk) / 2;
    
    return min(query(&(*tree)->left, pp, sr, zp, zk), query(&(*tree)->right, sr + 1, pk, zp, zk));
}

void aktualizuj(int ind, ll dp) {
    insert(&tree, 1, R, tab[ind] + q, dp - (ind + 1));
}

int main() {

    ios_base::sync_with_stdio(0);
    cin.tie(0);

    tree = (Node*) malloc(sizeof(struct Node));
    tree->value = INF;

    cin >> n;
    
    for (int i = 1; i <= n; ++i) {
        cin >> tab[i];
        tab[i] += tab[i - 1];
        
        mini = min(mini, tab[i]);
        maxi = max(maxi, tab[i]);
    }
    
    if (tab[n] < 0) {
        puts ("-1");
        return 0;
    }
    
    R = 1;
    while (R < (maxi - mini + 1)) {
        R <<= 1;
    }
    q = (1 - mini);
    
    debug {
        printf ("R=%lld q=%lld\n", R, q);
    }
    
    aktualizuj(0, 0);
    
    for (int i = 1; i <= n; ++i) {
        dp[i] = query(&tree, 1, R, 1, tab[i] + q);
        dp[i] += i;
        
        if (dp[i] >= n) {
            dp[i] = INF;
        }
        
        debug {
            fprintf(err, "i=%d dp[i]=%lld\n", i, dp[i]);
        }
        
        aktualizuj(i, dp[i]);
    }
    
    printf ("%lld\n", dp[n]);

    return 0;
}
/*
17
2 -5 0 2 0 0 0 4 0 0 -1 4 0 0 0 0 -3
*/