#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
const int mod=998244353;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){assert(!a.empty());T ans=a[0]-a[0];for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}

#line 1 "structure/convex-hull-trick/dynamic-li-chao-tree.hpp"
/**
 * @brief Dynamic-Li-Chao-Tree
 * @docs docs/dynamic-li-chao-tree.md
*/
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;

  DynamicLiChaoTree() : root{nullptr} {}

  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(x_l >= t_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(t_l >= x_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;
    }
  }

  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));
  }

  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;
  }

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

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

void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,0,t) solve();
}

void solve(){
	ll N;
	cin>>N;
	vector<ll> Q(N);
	rep(i,0,N) cin>>Q[i];
	DynamicLiChaoTree<ll,-101010,101010,ILL> D;
	D.add_line(0,0);
	rep(i,0,N){
		auto tmp=-D.query(Q[i]);
		D.add_line(-Q[i],-tmp);
	}
	cout<<-D.query(0)<<"\n";
}