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///MEMENTO MEMO, MEMENTO LONG LONG
#include <bits/stdc++.h>

#define DEBUG if(0)
#define COUT cout << "\e[36m"
#define ENDL "\e[39m" << endl
#define VAR(v) " [\e[32m" << #v << "\e[36m=\e[91m" << v << "\e[36m] "

using namespace std;
typedef long long LL;

const int MAXINT = 1e9+1;
int n, m;
vector<int> city, dp;

struct Segtree
{
    int l;
    vector<int> treeVec;

    void print()
    {
        DEBUG
        {
            int k = 1, j= 1;
            for (int i = 1; i < 2*l; ++i) {
                COUT << treeVec[i] << " ";
                j++;
                if(j > k)
                {
                    COUT << ENDL;
                    k*=2;
                    j = 1;
                }

            }
        }
    }

    int queryMin(int b, int e)
    {
        b += l;
        e += l;
        int out = MAXINT;
        //DEBUG COUT<< VAR(b) << VAR(e) << VAR(l) << VAR(m) << ENDL;
        while(b <= e)
        {
            if(b%2 == 1)
                out = min(out, treeVec[b]);
            if(e%2 == 0)
                out = min(out, treeVec[e]);
            b = (b+1)/2;
            e = (e-1)/2;
        }
        return out;
    }

    void setMin(int pos, int val)
    {
        pos += l;
        while(pos > 0)
        {
            treeVec[pos] = min(treeVec[pos], val);
            pos/=2;
        }
    }

    Segtree(/**size is m*/)
    {
        l = 1;
        while(l < m)
            l*= 2;

        treeVec.resize(2*l, MAXINT);
    }
};

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;
    city.resize(n+1);
    vector<LL> suff(n+2);

    for (int i = 1; i <= n; ++i) {
        cin >> city[i];
    }
    map<LL, int> suffToId;
    suffToId[0] = -1;
    for (int i = n; i >= 0; --i) {
        suff[i] = city[i]+((i+1 < n+1)? suff[i+1] : 0);
        suffToId[suff[i]] = -1;
    }
    map<LL,int>::iterator it = suffToId.begin();
    for (int i = 0; it != suffToId.end(); it++, i++) {
        it->second = i;
    }
    m = suffToId.size();
    DEBUG
    {
        DEBUG COUT << "CITY" << ENDL;
        for(auto el : city)
            COUT << el << " ";
        COUT << ENDL;
        DEBUG COUT << "SUFF" << ENDL;
        for(auto el : suff)
            COUT << el << " ";
        COUT << ENDL;
        DEBUG COUT << "SUFFtoID" << ENDL;
        for(auto el : suffToId)
            COUT << "[" << el.first << ":" << el.second << "] ";
        COUT << ENDL;
    }
    dp.resize(n+1, MAXINT);
    dp[0] = 0;

    Segtree tree;
    for (int i = 1; i <= n; ++i)
    {
        ///set dp[i-1]+n-i on tree(sufftoid[suff[i]])
        tree.setMin(suffToId[suff[i]], dp[i-1]+(n-i));
        ///dp[i] = tree.min(B, sufftoid.size()-1)  -(n-i)
        dp[i] = tree.queryMin(suffToId[suff[i+1]], m-1)-(n-i);

        DEBUG COUT << VAR(i) << VAR(dp[i]) <<  ENDL;
        DEBUG tree.print();
        DEBUG COUT << ENDL;
    }
    cout << ((dp[n] > n-1)? -1 : dp[n]) << "\n";
    return 0;
}