#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
const int N = 1000000;
const ll INF = 1000000000000000000LL;
ll a[N+5];
ll dp[N+5];
struct line{
ll k, n;
ll eval(int x){ return k*x + n; }
} seg[4*N+5];
ll query(int node, int l, int r, int i){
ll g = seg[node].eval(i);
if(l == r) return g;
int mid = (l+r)/2;
if(i <= mid) return min(g, query(node*2, l, mid, i));
return min(g, query(node*2+1, mid+1, r, i));
}
stack <tuple <line, int, int>> rev;
void brisi(int i){
while(!rev.empty() && get<2>(rev.top()) == i){
seg[get<1>(rev.top())] = get<0>(rev.top());
rev.pop();
}
}
void upd(int node, int l, int r, line g, int i){
int mid = (l+r)/2;
if(g.eval(mid) < seg[node].eval(mid)){
rev.push({seg[node], node, i});
swap(g, seg[node]);
}
if(l == r) return;
if(seg[node].eval(l) > g.eval(l)) upd(node*2, l, mid, g, i);
else upd(node*2+1, mid+1, r, g, i);
}
int main(){
ios_base::sync_with_stdio(false), cin.tie(0);
cout.precision(10);
cout << fixed;
int n;
cin >> n;
for(int i=1; i<=n; i++){
cin >> a[i];
}
reverse(a+1, a+1+n);
for(int i=1; i<=4*n; i++) seg[i].n = INF;
stack <int> st;
for(int i=1; i<=n; i++){
while(!st.empty() && a[st.top()] <= a[i]){
brisi(st.top());
st.pop();
}
line h;
h.k = a[i];
h.n = 0;
if(!st.empty()){
h.n = dp[st.top()];
}
upd(1, 1, n, h, i);
st.push(i);
dp[i] = query(1, 1, n, i);
}
cout << dp[n] << "\n";
return 0;
}
