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

using namespace std;
using namespace atcoder;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n) for(int i = 0; i < (int)(n); ++i)
#define rep2(i, n) for(int i = 0; i < (int)(n); ++i)
#define rep3(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep4(i, a, b, c) for(int i = (a); i < (int)(b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)

#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i)
#define ALL(a) a.begin(), a.end()
#define Sort(a) sort(a.begin(), a.end())
#define RSort(a) sort(a.rbegin(), a.rend())

typedef long long int ll;
typedef unsigned long long ul;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<char> vc;
typedef vector<string> vst;
typedef vector<double> vd;
typedef vector<long double> vld;
typedef pair<long long, long long> P;

template<class T> long long sum(const T& a){ return accumulate(a.begin(), a.end(), 0LL); }
template<class T> auto min(const T& a){ return *min_element(a.begin(), a.end()); }
template<class T> auto max(const T& a){ return *max_element(a.begin(), a.end()); }

const long long MINF = 0x7fffffffffff;
const long long INF = 0x1fffffffffffffff;
const long long MOD = 998244353;
const long double EPS = 1e-9;
const long double PI = acos(-1);
 
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p){ is >> p.first >> p.second; return is; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){ os << "(" << p.first << ", " << p.second << ")"; return os; }
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for(T &in : v) is >> in; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v){ for(int i = 0; i < (int) v.size(); ++i){ os << v[i] << (i + 1 != (int) v.size() ? " " : ""); } return os; }
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp){ for(auto &[key, val] : mp){ os << key << ":" << val << " "; } return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int)st.size(); ++i){ os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, queue<T> q){ while(q.size()){ os << q.front() << " "; q.pop(); } return os; }
template <typename T> ostream &operator<<(ostream &os, deque<T> q){ while(q.size()){ os << q.front() << " "; q.pop_front(); } return os; }
template <typename T> ostream &operator<<(ostream &os, stack<T> st){ while(st.size()){ os << st.top() << " "; st.pop(); } return os; }
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq){ while(pq.size()){ os << pq.top() << " "; pq.pop(); } return os; }

template<class T, class U> inline T vin(T& vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; }
template<class T> inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; }
template<class... T> void in(T&... a){ (cin >> ... >> a); }
void out(){ cout << '\n'; }
template<class T, class... Ts> void out(const T& a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T, class U> void inGraph(vector<vector<T>>& G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; ++i){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } }

template<typename T, T x_low, T x_high, T id>
struct DynamicLiChaoTree{
    struct Line{
        T a, b;

        Line(T _a, T _b) : a(_a), b(_b) {}

        inline T get(T x) const {
            return a * x + b;
        }
    };

    struct Node{
        Line x;
        Node *l, *r;

        Node(const Line &x) : x{x}, l{nullptr}, r{nullptr} {}
    };

    Node *root = nullptr;

    DynamicLiChaoTree() {}

private:
    Node *add_line_(Node *t, Line &x, const T &l, const T &r, const T &x_l, const T &x_r){
        if(!t){
            return new Node(x);
        }

        T t_l = t->x.get(l), t_r = t->x.get(r);

        if(t_l <= x_l && t_r <= x_r){
            return t;
        }else if(t_l >= x_l && t_r >= x_r){
            t->x = x;
            return t;
        }else{
            T m = (l + r) / 2;
            if(m == r) --m;
            T t_m = t->x.get(m), x_m = x.get(m);
            if(t_m > x_m){
                swap(t->x, x);
                if(t_l <= x_l){
                    t->l = add_line_(t->l, x, l, m, t_l, t_m);
                }else{
                    t->r = add_line_(t->r, x, m + 1, r, t_m + x.a, t_r);
                } 
            }else{
                if(x_l <= t_l){
                    t->l = add_line_(t->l, x, l, m, x_l, x_m);
                }else{
                    t->r = add_line_(t->r, x, m + 1, r, x_m + x.a, x_r);
                } 
            }
            return t;
        }
    }

    Node *add_segment_(Node *t, Line &x, const T &a, const T &b, const T &l, const T &r, const T &x_l, const T &x_r){
        if(r < a || b < l) return t;
        if(a <= l && r <= b){
            Line y{x};
            return add_line_(t, y, l, r, x_l, x_r);
        }
        if(t){
            T t_l = t->x.get(l), t_r = t->x.get(r);
            if(t_l <= x_l && t_r <= x_r) return t;
        }else{
            t = new Node(Line(0, id));
        }

        T m = (l + r) / 2;
        if(m == r) --m;
        T x_m = x.get(m);
        t->l = add_segment_(t->l, x, a, b, l, m, x_l, x_m);
        t->r = add_segment_(t->r, x, a, b, m + 1, r, x_m + x.a, x_r);
        return t;
    }

    T query_(const Node *t, const T &l, const T &r, const T &x_c) const {
        if(!t) return id;
        if(l == r) return t->x.get(x_c);
        T m = (l + r) / 2;
        if(m == r) --m;
        if(x_c <= m){
            return min(t->x.get(x_c), query_(t->l, l, m, x_c));
        }else{
            return min(t->x.get(x_c), query_(t->r, m + 1, r, x_c));
        }
    }

public:
    void add_line(const T &a, const T &b){
        Line x(a, b);
        root = add_line_(root, x, x_low, x_high, x.get(x_low), x.get(x_high));
    }

    void add_segment(const T &l, const T &r, const T &a, const T &b){
        Line x(a, b);
        root = add_segment_(root, x, l, r - 1, x_low, x_high, x.get(x_low), x.get(x_high));
    }

    T query(const T &x) const {
        return query_(root, x_low, x_high, x);
    }
};

ll n;
vll q;

void input(){
    in(n);
    vin(q, n);
}

void solve(){
    DynamicLiChaoTree<ll, -(1 << 30), 1 << 30, INF> dlct;
    vll dp(n);
    rep(i, n){
        chmax(dp[i], dlct.query(q[i]) * -1);
        dlct.add_line(-1 * (q[i]), dp[i] * -1);
    }
    out(max(dp));
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);
    
    input();
    solve();
}