// "Complex numbers are better than pears."
// "Always use complex numbers when possible."
// "And plus real numbers are complex numbers anyway so you'll be using them."
// "69 is the largest number you can factorial on a calculator."
// "Therefore, always make your code 69 lines if possible."
// - Some Y1 Rafflesian
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define re real()
#define im imag()
#define mp make_pair
#define pb push_back
#define speed ios_base::sync_with_stdio(false); cin.tie(0)
#define stMx(a,b) a = max(a,b)
#define stMn(a,b) a = min(a,b)
typedef complex<int> ii;
typedef vector<int> vi;
typedef set<int> si;
typedef vector<ii> vii;
typedef set<ii> sii;
#define REP(i, a, b) for(int i = a; i < b; i++)
#define float long double
deque<ii> dq;
int f(ii line, int x) {
return line.re * x + line.im;
}
int query(int x) {
while(dq.size() > 1) {
if(f(dq[0], x) < f(dq[1], x)) dq.pop_front();
else break;
}
return f(dq[0], x);
}
float intersect(int a, int b, int c, int d) {
return (float)(d - b) / (a - c);
}
float intersect(ii p1, ii p2) {
return intersect(p1.re, p1.im, p2.re, p2.im);
}
void ins(int m, int c) {
ii line = ii(m, c);
while(dq.size() > 1) {
int s = dq.size();
if(intersect(dq[s - 1], line) <= intersect(dq[s - 2], line)) dq.pop_back();
else break;
}
dq.push_back(line);
}
int32_t main() {
int N; cin >> N; int T[N], pre[N], nd[N], dp[N];
cin >> T[0]; pre[0] = T[0];
REP(i, 1, N) {
cin >> T[i];
pre[i] = max(T[i], pre[i-1]);
}
ins(-1 * N, 0);
REP(i, 0, N) {
if(i == 0 || pre[i - 1] < T[i]) {
dp[i] = -1 * query(T[i]);
int ptr = i;
while(ptr < N && T[ptr] <= T[i]) ptr++;
ins(ptr - N, -1 * dp[i]);
} else {
dp[i] = dp[i - 1];
}
}
cout << dp[N-1];
}
