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#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define pb push_back
#define mp make_pair
#define all(a) begin(a),end(a)
#define FOR(x,val,to) for(int x=(val);x<int((to));++x)
#define FORE(x,val,to) for(auto x=(val);x<=(to);++x)
#define FORR(x,arr) for(auto &x: arr)
#define FORS(x,plus,arr) for(auto x = begin(arr)+(plus); x != end(arr); ++x)
#define FORREV(x,plus,arr) for(auto x = (arr).rbegin()+(plus); x !=(arr).rend(); ++x)
#define REE(s_) {cout<<s_<<'\n';exit(0);}
#define GET(arr) for(auto &i: (arr)) sc(i)
#define whatis(x) cerr << #x << " is " << (x) << endl;
#define e1 first
#define e2 second
#define INF 0x7f7f7f7f
typedef std::pair<int,int> pi;
typedef std::vector<int> vi;
typedef std::vector<std::string> vs;
typedef int64_t ll;
typedef uint64_t ull;
#define umap unordered_map
#define uset unordered_set
using namespace std;
using namespace __gnu_pbds;

#ifdef ONLINE_JUDGE
#define whatis(x) ;
#endif
#ifdef _WIN32
#define getchar_unlocked() _getchar_nolock()
#define _CRT_DISABLE_PERFCRIT_LOCKS
#endif
template<class L, class R> ostream& operator<<(ostream &os, map<L, R> P) { for(auto const &vv: P)os<<"("<<vv.first<<","<<vv.second<<")"; return os; }
template<class T> ostream& operator<<(ostream &os, set<T> V) { os<<"[";for(auto const &vv:V)os<<vv<<","; os<<"]"; return os; }
template<class T> ostream& operator<<(ostream &os, vector<T> V) { os<<"[";for(auto const &vv:V)os<<vv<<","; os<<"]"; return os; }
template<class L, class R> ostream& operator<<(ostream &os, pair<L, R> P) { os<<"("<<P.first<<","<<P.second<<")"; return os; }
inline int fstoi(const string &str){auto it=str.begin();bool neg=0;int num=0;if(*it=='-')neg=1;else num=*it-'0';++it;while(it<str.end()) num=num*10+(*it++-'0');if(neg)num*=-1;return num;}
inline void getch(char &x){while(x = getchar_unlocked(), x < 33){;}}
inline void getstr(string &str){str.clear(); char cur;while(cur=getchar_unlocked(),cur<33){;}while(cur>32){str+=cur;cur=getchar_unlocked();}}
template<typename T> inline bool sc(T &num){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){if(c == EOF) return false;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; return true;}template<typename T, typename ...Args> inline void sc(T &num, Args &...args){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; sc(args...); }
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; //s.find_by_order(), s.order_of_key() <- works like lower_bound
template<typename T> using ordered_map = tree<T, int, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define N 524288

// wartości akurat są intami for sure
int t[N*2];
int nn;

int query(int l, int r){
    int res = INF;
    for(l+=nn, r+=nn; l<r; l>>=1, r>>=1){
        if(l&1)
            res = min(res,t[l++]);
        if(r&1)
            res = min(res,t[--r]);
    }
    return res;
}

void modify(int p, int val){
    /* for(t[p += n] = val; p > 1; p>>=1) */
    p += nn;
    t[p] = min(t[p], val);
    for(; p > 1; p>>=1)
        /* t[p>>1] = max(t[p] , t[p^1]); */ // hmmmmmmmm
        t[p>>1] = min(t[p] , t[p^1]);
}

// dla segtree n musi być n + 1 tak na prawdę, bo jeszcze 0 odpowiadające pre[-1]

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
    /* int n; */
    int n;
    sc(n);
    nn = n + 1;
    int a[n];
    GET(a);
    vector<ll> vec;
    ll pre[n];
    pre[0] = a[0];
    // forgot to push_back pre[0]
    vec.pb(pre[0]);
    FOR(i,1,n){
        pre[i] = a[i] + pre[i-1];
        vec.pb(pre[i]);
    }
    sort(all(vec));
    vec.erase(unique(all(vec)),vec.end());
    // forgot to build segtree btw
    memset(t,127,sizeof t); // fine with t[0] being whatever
    // -> res inf on sample lol
    int dp[n+1];
    memset(dp,127,sizeof dp);
    dp[0] = 0; // everything till first fabryka włącznie is 0 wsm
    int _pos = lower_bound(all(vec),0) - vec.begin();
    /* whatis(_pos) */
    modify(_pos, 0);
    FOR(i,0,n){
        /* whatis(query(0, 0)); */
        /* whatis(query(0, 1)); */
        /* whatis(query(0, 2)); */
        int pos = lower_bound(all(vec),pre[i]) - vec.begin();
        /* if(a[i] > 0){ */
            /* ll crs = 0; */
            /* for(int x = i; x >= 0; --x){ */
            /*     crs += a[x]; */
            /*     if(dp[x] == INF) */
            /*         continue; */
            /*     if(crs >= 0){ */
            /*         dp[i + 1] = min(dp[i + 1], dp[x] + i - x); */
            /*     } */
            /* } */
            /* dp[i + 1] = i + query(0, pos); */
            // forgot that this iterative segtree has exclusive r
            /* whatis(pos) */
            /* whatis(query(0, pos + 1)) */
            dp[i + 1] = i + query(0, pos + 1);
            dp[i + 1] = min(dp[i + 1], INF);
            // za i + 1 modify
            /* modify(pos, a[i] - i); */
            /* modify(pos, dp[i + 1] - i); */
            // pre[x - 1] correct
            modify(pos, dp[i + 1] - (i + 1));
        /* } */
        /* whatis(i+1) */
        /* whatis(dp[i+1]) */
    }
    /* cout << dp[n] << '\n'; */
    cout << (dp[n] == INF ? -1 : dp[n]) << '\n';
    /* cout << (dp[n] >= INF ? -1 : dp[n]) << '\n'; */
    // XD, gj, first compile and run -> good result on sample
    // po upgradzie do O(nlogn) sadly not again xd
    // fixed stuff around segtree (max -> min) i git
}