#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
istream &operator>>(istream &is, modint &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint &a) { return os << a.val(); }
istream &operator>>(istream &is, modint998244353 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint998244353 &a) { return os << a.val(); }
istream &operator>>(istream &is, modint1000000007 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint1000000007 &a) { return os << a.val(); } 

typedef long long ll;
typedef vector<vector<int>> Graph;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define rep(i,n) for (int i = 0;i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define my_sort(x) sort(x.begin(), x.end())
#define my_max(x) *max_element(all(x))
#define my_min(x) *min_element(all(x))
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; }
const int INF = (1<<30) - 1;
const ll LINF = (1LL<<62) - 1;
const int MOD = 998244353;
const int MOD2 = 1e9+7;
const double PI = acos(-1);
vector<int> di = {1,0,-1,0};
vector<int> dj = {0,1,0,-1};

#ifdef LOCAL
#  include <debug_print.hpp>
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

// ライブラリ
// https://kopricky.github.io/code/DataStructure_Advanced/dynamic_convex_hull_trick.html
// 解法
// https://qiita.com/Series_205/items/05bd22a4e78527cb29dc
template<typename T> class ConvexHullTrick {
private:
    struct node {
        node *left, *right;
        static const T inf = numeric_limits<T>::max();
        T a, b;
        node() : node(0, inf){}
        node(const T _a, const T _b)
            : left(nullptr), right(nullptr), a(_a), b(_b){}
        T f(const T x) const { return a * x + b; }
    };
    static void swap(node *x, node *y){
        std::swap(x->a, y->a), std::swap(x->b, y->b);
    }
    void _add_line(node *cur, node *nw, T l, T r){
        while(true){
            if(nw->f(l) < cur->f(l)) swap(cur, nw);
            if(cur->f(r - 1) <= nw->f(r - 1)) break;
            const T mid = (l + r) / 2;
            if(cur->f(mid) <= nw->f(mid)){
                if(!cur->right){
                    cur->right = new node(*nw);
                    break;
                }else{
                    cur = cur->right, l = mid;
                }
            }else{
                swap(cur, nw);
                if(!cur->left){
                    cur->left = new node(*nw);
                    break;
                }else{
                    cur = cur->left, r = mid;
                }
            }
        }
    }
    T query(node *cur, const T k, T l, T r) const {
        T ans = numeric_limits<T>::max();
        while(cur){
            ans = min(ans, cur->f(k));
            const T mid = (l + r) / 2;
            if(k < mid){
                cur = cur->left, r = mid;
            }else{
                cur = cur->right, l = mid;
            }
        }
        return ans;
    }
    void clear(node *cur){
        if(cur->left) clear(cur->left);
        if(cur->right) clear(cur->right);
        delete cur;
    }
    const T lpos, rpos;
    node *root;
public:
    ConvexHullTrick(const T _lpos, const T _rpos) : lpos(_lpos), rpos(_rpos), root(new node()){
        assert(lpos < rpos);
    }
    // ~ConvexHullTrick(){ clear(root); }
    // f(x) = a * x + b を挿入
    void add_line(const T a, const T b){
        node nw(a, b);
        return _add_line(root, &nw, lpos, rpos);
    }
    // x = k での最小値
    T query(const T k) const {
        return query(root, k, lpos, rpos);
    }
};

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    int N; cin >> N;
    vector<ll> Q(N+1,0);
    rep(i,N) cin >> Q[i+1];
    ConvexHullTrick<ll> seg(-303030, 303030);
    vector<ll> dp(N + 1);
    dp[0] = 0;
    seg.add_line(-Q[0], -dp[0]);
    rep(i,N+1){
        dp[i] = -seg.query(Q[i]);
        seg.add_line(-Q[i], -dp[i]);
    }
    ll ans = -LINF;
    rep(i,N+1) chmax(ans, dp[i]);
    cout << ans << endl;
}