//#include <bits/stdc++.h>

#include <iostream>
#include <algorithm>

#include <bitset>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <cstring>
#include <string>
#include <utility>
#include <array>
#include <complex>
#include <valarray>

#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>

#include<memory>


using namespace std;
#define int long long

typedef long long ll;
typedef unsigned long long ull;
//typedef unsigned __int128 HASH;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll,int> plli;
typedef pair<double,int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int,pii> pipii;
typedef pair<ll,pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n);i>0;i--)
#define rrep2(i,a,b) for (int i=(a);i>b;i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1<<30;
const ll INFLL = 1LL<<62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
//const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w) (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

//debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...) DUMPOUT<<#__VA_ARGS__<<" :["<<__FUNCTION__<<":"<<__LINE__<<"]"<<endl; DUMPOUT<<"    "; dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() {DUMPOUT << endl;};

template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) == 0) DUMPOUT << " ";
    else DUMPOUT << ", ";
    dump_func(std::move(tail)...);
}

//ostream
template<typename T> ostream& operator << (ostream& os, vector<T>& vec) {
    os << "["; for (int i = 0; i<vec.size(); i++) os << vec[i] << (i + 1 == vec.size() ? "" : ", "); os << "]";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, pair<T, U>& pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, map<T, U>& map_var) {
    os << "[";
    for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
        os << "(" << itr->first << ", " << itr->second << ")"; itr++;  if(itr != map_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

template<typename T> ostream& operator << (ostream& os, set<T>& set_var) {
    os << "[";
    for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
        os << *itr; ++itr; if(itr != set_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

int w;
vector<int> a(100000 + 5);
vector<int> ex;

struct segtree {
    int size;
    vector<long long> node;

    segtree (int n) : size(1) {
        while (size < n) size *= 2;
        node.resize(2 * size - 1, INFLL / 2);
    }

    void update(int k, int a) {
        k += size - 1;
        node[k] = a;
        while (k > 0){
            k = (k - 1) / 2;
            node[k] = min(node[2 * k + 1], node[2 * k + 2]);
        }
    }
    //[queryL: queryR)
    long long get(int queryL, int queryR, int k = 0, int nodeL = 0, int nodeR = -1) {
        if (nodeR == -1) nodeR = size;
        if (nodeR <= queryL || queryR <= nodeL) return INFLL;//初期値より大きく
        if (queryL <= nodeL && nodeR <= queryR) return node[k];
        else{
            int nodeM = (nodeL + nodeR) / 2;
            long long vl = get(queryL, queryR, 2 * k + 1, nodeL, nodeM);
            long long vr = get(queryL, queryR, 2 * k + 2, nodeM, nodeR);
            return min(vl, vr);
        }
    }
};

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> w;
  segtree segr(w);
  segtree segl(w);
  vector<int> diff_sumr(w), diff_suml(w);
  vector<int> minus_pos;
  bool plus = false;
  rep(i, w) {
    cin >> a[i];
    if (a[i] == 0) ex.push_back(i);
    if (a[i] > 0) plus = true;
    if (a[i] < 0) {
      minus_pos.push_back(i);
    }
  }
  if (ex.size() == 0 || !plus) {
    cout << 0 << endl;
    return 0;
  }
  int ans = 0;
  if (minus_pos.size() == 0) {
    rep(i, w) {
      if (a[i] > 0) ans += a[i];
    }
    cout << ans << endl;
    return 0;
  }
  rep2(i, 1, minus_pos.size()) {
    int cur = minus_pos[i];
    int pre = minus_pos[i - 1];
    diff_sumr[cur] = cur - pre;
  }
  rrep2(i, (int)minus_pos.size() - 2, -1) {
    int cur = minus_pos[i];
    int pre = minus_pos[i + 1];
    diff_suml[cur] = pre - cur;
  }
  rep(i, w - 1) diff_sumr[i + 1] += diff_sumr[i];
  rep(i, w) {
    if (a[i] < 0) {
      segr.update(i, -a[i] - diff_sumr[i]);
    }
  }
  rrep2(i, w - 1, 0) diff_suml[i - 1] += diff_suml[i];
  rrep2(i, w - 1, -1) {
    if (a[i] < 0) {
      segl.update(i, -a[i] - diff_suml[i]);
    }
  }

  rep(i, w) {
    if (a[i] <= 0) continue;
    int exidx = lower_bound(all(ex), i) - ex.begin();
    int exposl = -1;
    int exposr = -1;
    int minusidx = lower_bound(all(minus_pos), i) - minus_pos.begin();
    int mnposl = -1;
    int mnposr = -1;
    if (minusidx == 0) {
      mnposr = minus_pos[minusidx];
    }
    else if (minusidx == minus_pos.size()) {
      mnposl = minus_pos[minusidx - 1];
    }
    else {
      mnposl = minus_pos[minusidx - 1];
      mnposr = minus_pos[minusidx];
    }
    if (exidx == 0) {
      exposr = ex[exidx];
      if (mnposr == -1 || mnposr > exposr) {
         //cerr << "1 : " << i << " " << a[i] << endl;
         ans += a[i];
      }
      else {
        int cnt = segr.get(i, exposr + 1) + diff_sumr[mnposr] - (mnposr - i);
        if (cnt < 0) continue;
        //cerr << "2 : " << i << " " << min(a[i], cnt) << endl;
        ans += min(a[i], cnt);
      }
    }
    else if (exidx == ex.size()) {
      exposl = ex[exidx - 1];
      if (mnposl < exposl) {
        ans += a[i];
        //cerr << "3 : " << i << " " << a[i] << endl;
      }
      else {
        int cnt = segl.get(exposl, i + 1) + diff_suml[mnposl] - (i - mnposl);
        if (cnt < 0) continue;
        //cerr << "4 : " << i << " " << min(a[i], cnt) << endl;
        ans += min(a[i], cnt);
      }
    }
    else {
      exposl = ex[exidx - 1];
      exposr = ex[exidx];
      if (mnposl < exposl || exposr < mnposr || mnposr == -1) {
        //cerr << "5 : " << i << " " << a[i] << endl;
        ans += a[i];
      }
      else {
        int cntl = segl.get(exposl, i + 1) + diff_suml[mnposl] - (i - mnposl);
        int cntr = segr.get(i, exposr + 1) + diff_sumr[mnposr] - (mnposr - i);
        if (cntl < 0 && cntr < 0) continue;
        if (cntl < 0) {
          //cerr << "6 : " << i <<  " " << min(a[i], cntr) << endl;
          ans += min(a[i], cntr);
        }
        else if (cntr < 0) {
          //cerr << "7 : " << i << " " << min(a[i], cntl) << endl;
          ans += min(a[i],  cntl);
        }
        else {
          //cerr << "8 : " << i << " " << min({a[i], max(cntl, cntr)}) << endl;
          ans += min(a[i], max(cntl, cntr));
        }
      }
    }
  }
  cout << ans << endl;
}



Measured memory_bytes: 10296