#include <bits/stdc++.h>
using namespace std;
const int N = 1'000'000 + 10;
int n;
int a[N];
struct Line {
long long a = 0, b = 0;
Line() {};
Line(long long a, long long b) : a(a), b(b) {}
long long cal(const long long& x) { return a * x + b; }
};
inline bool bad(const Line& A, const Line& B, const Line& C) {
return 1.0 * (C.b - A.b) / (A.a - C.a) < 1.0 * (B.b - A.b) / (A.a - B.a);
}
const long long MAX = 1'000'000'000'000'000'000;
struct CHT {
vector<Line> st = {};
int bot = 0;
void addLine(const Line& cur) {
for (; st.size() > 1 && bad(st.end()[-2], st.end()[-1], cur); st.pop_back());
st.push_back(cur);
bot = min(bot, (int)st.size() - 1);
}
long long get(long long x) {
if(st.empty()) return MAX;
for (; bot < (int)st.size() - 1 && st[bot].cal(x) > st[bot + 1].cal(x); ++bot);
return st[bot].cal(x);
}
};
long long f[N];
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> a[i];
reverse(a + 1, a + n + 1);
vector<int> q;
for (int i = 1; i <= n; ++i) {
while (q.size() && a[q.back()] <= a[i]) q.pop_back();
q.push_back(i);
}
CHT cht;
cht.addLine({a[q[0]], 0});
for (int i = 1; i <= (int)q.size(); ++i) {
f[i] = cht.get(q[i - 1]);
if (i < (int)q.size()) cht.addLine({a[q[i]], f[i]});
}
cout << f[q.size()] << "\n";
}
